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Rehabilitation Treatment Taxonomy: Implications and Continuations

      Abstract

      In relation to the conceptual framework for a rehabilitation treatment taxonomy (RTT), which has been proposed in other articles in this supplement, this article discusses a number of issues relevant to its further development, including creating distinctions within the major target classes; the nature and quantity of allowable targets of treatment; and bracketing as a way of specifying (1) the skill or knowledge taught; (2) the nature of compensation afforded by changes in the environment, assistive technology, and orthotics/prosthetics; and (3) the ingredients in homework a clinician assigns. Clarification is provided regarding the role of the International Classification of Functioning, Disability and Health, focusing a taxonomy on ingredients versus other observable aspects of treatment, and regarding our lack of knowledge and its impact on taxonomy development. Finally, this article discusses the immediate implications of the work to date and presents the need for rehabilitation stakeholders of all disciplines to be involved in further RTT development.

      Keywords

      List of abbreviations:

      ADL (activities of daily living), ICF (International Classification of Functioning, Disability and Health), RTT (rehabilitation treatment taxonomy), SCI (spinal cord injury)
      Rehabilitation is effective some of the time, for some problems of some patients, and that is the reason that patients return and third-party payers keep paying the not inconsequential fees that the rehabilitation enterprise charges. The third party payers, however, increasingly ask for evidence that what they pay for works and have started to refuse to pay for those interventions for which no evidence of effectiveness exists. Unfortunately, we have such evidence of effectiveness for only a very limited number of treatments, a position not much different from that of the rest of health care. Even in those limited instances, we may only know that a particular treatment or group of treatments being delivered under a particular label (for instance, “inpatient spinal cord injury [SCI] occupational therapy”) has better effects than the absence of any treatment, but we do not necessarily know the active ingredients comprised under those labels, and which one(s) is beneficial or even essential for which outcomes. Generally, we do not know what is being offered as part of multidisciplinary rehabilitation interventions, with what ingredients, and with what direct and indirect causal effects, only some of which may coincide with the clinical goals and targets that were intended to be addressed by treatment.
      • Whiteneck G.
      • Gassaway J.
      • Dijkers M.
      • et al.
      The SCIRehab project: treatment time spent in SCI rehabilitation. Inpatient treatment time across disciplines in spinal cord injury rehabilitation.
      It has probably been more than 4 decades since someone first used the term “black box” to describe the nature of multidisciplinary rehabilitation; and in the years since, the sides of the box have not become less opaque.
      In short, we have limited insight into what our treatments are, and what are feasible ways of operationalizing and quantifying them for dosing in clinical practice, or for research on treatments. As a field, we (clinicians, researchers, educators, and other stakeholders, collectively) have largely focused our research on the measurement of inputs (admission deficits and other patient characteristics) and outcomes, rather than treatments.
      • Dijkers M.
      • Kropp G.C.
      • Esper R.M.
      • Yavuzer G.
      • Cullen N.
      • Bakdalieh Y.
      Quality of intervention research reporting in medical rehabilitation journals.
      • van Heugten C.
      • Gregório G.W.
      • Wade D.
      Evidence-based cognitive rehabilitation after acquired brain injury: a systematic review of content of treatment.
      The way out of this problem is often seen to be the creation of a taxonomy of rehabilitation interventions, and in the literature, there are quite a few ad hoc classifications of medical rehabilitation interventions in particular areas and/or for particular diagnostic groups.
      • van Langeveld S.A.
      • Post M.W.
      • van Asbeck F.W.
      • Postma K.
      • Ten Dam D.
      • Pons K.
      Development of a classification of physical therapy, occupational therapy and sports therapy interventions to document mobility and self-care in spinal cord injury rehabilitation.
      • Finger M.E.
      • Cieza A.
      • Stoll J.
      • Stucki G.
      • Huber E.O.
      Identification of intervention categories for physical therapy, based on the International Classification of Functioning, Disability and Health: a Delphi exercise.
      • Pomeroy V.M.
      • Niven D.S.
      • Barrow S.
      • Faragher E.B.
      • Tallis R.C.
      Unpacking the black box of nursing and therapy practice for post-stroke shoulder pain: a precursor to evaluation.
      • Niemeijer A.S.
      • Smits-Engelsman B.C.
      • Reynders K.
      • Schoemaker M.M.
      Verbal actions of physiotherapists to enhance motor learning in children with DCD.
      • Sherman K.J.
      • Dixon M.W.
      • Thompson D.
      • Cherkin D.C.
      Development of a taxonomy to describe massage treatments for musculoskeletal pain.
      • Grobe S.J.
      • Hughes L.C.
      The conceptual validity of a taxonomy of nursing interventions.
      • Smallfield S.
      • Karges J.
      Classification of occupational therapy intervention for inpatient stroke rehabilitation.
      They tend to have many shortcomings, a major one of which is “goal-oriented language”
      • Zanca J.M.
      • Dijkers M.P.
      Describing what we do: a qualitative study of clinicians' perspectives on classifying rehabilitation interventions.
      : a tendency to name an intervention or group of interventions based on the deficit selected for treatment (for instance, “gait therapy”), and assuming that what goes under that particular label is known and is the same from one facility to the next and from one clinician to the next.
      In the other articles included in this supplement,
      • Dijkers M.P.
      • Hart T.
      • Tsaousides T.
      • Whyte J.
      • Zanca J.M.
      Treatment taxonomy for rehabilitation: past, present, and prospects.
      • Whyte J.
      • Dijkers M.P.
      • Hart T.
      • et al.
      Development of a theory-driven rehabilitation treatment taxonomy: conceptual issues.
      • Whyte J.
      Contributions of treatment theory and enablement theory to rehabilitation research and practice.
      • Hart T.
      • Tsaousides T.
      • Zanca J.M.
      • et al.
      Toward a theory-driven classification of rehabilitation treatments.
      the following points have been argued:
      • A comprehensive *taxonomy or similar classification of rehabilitation *treatment is needed to assist researchers, clinicians and educators, and other stakeholders in describing comprehensively and precisely what happens in the black box of rehabilitation and to help create the evidence base needed to improve treatments.
        • Dijkers M.P.
        • Hart T.
        • Tsaousides T.
        • Whyte J.
        • Zanca J.M.
        Treatment taxonomy for rehabilitation: past, present, and prospects.
        (Words and phrases that are specifically defined in supplemental appendix S1 [available on page A9 of this supplement and online at http://www.archives-pmr.org/] are marked with an asterisk and italicized when initially used.)
      • Any classification of rehabilitation interventions should be based on the *active ingredients that are used in them, specifically the *essential ingredients that characterize those interventions, rather than the patient deficit selected for treatment or other even more incidental aspects of the treatment.
        • Dijkers M.P.
        • Hart T.
        • Tsaousides T.
        • Whyte J.
        • Zanca J.M.
        Treatment taxonomy for rehabilitation: past, present, and prospects.
        • Whyte J.
        • Dijkers M.P.
        • Hart T.
        • et al.
        Development of a theory-driven rehabilitation treatment taxonomy: conceptual issues.
      • Active ingredients are only identified when one has a tripartite *treatment theory that links *treatment ingredients through a *mechanism of action to the *target of treatment, a specific aspect of functioning that the clinician wants to change.
        • Hart T.
        • Tsaousides T.
        • Zanca J.M.
        • et al.
        Toward a theory-driven classification of rehabilitation treatments.
        (This is illustrated in fig 1.) Note, however, that the clinician, starting with the need for change, reasons in the opposite direction of the causal chain in order to put it into play.
        • Hart T.
        • Tsaousides T.
        • Zanca J.M.
        • et al.
        Toward a theory-driven classification of rehabilitation treatments.
        The clinician typically takes the patient's strengths and weaknesses into account when making ingredient selection(s).
        Figure thumbnail gr1
        Fig 1Conceptual framework of the RTT at a glance. Abbreviation: AT, assistive technology.
      • Changes in the target of treatment can have repercussions for other aspects of functioning (as specified by *enablement theory), which may be a clinical *aim(s) downstream from the target of treatment.
        • Whyte J.
        Contributions of treatment theory and enablement theory to rehabilitation research and practice.
      • Rehabilitation treatments ranging from drugs to training of personal aides, and from assistive devices to instruction in activities of daily living (ADL), can be classified in groups and subgroups based on their shared active ingredients, which, as postulated in their treatment theories, tend to have characteristic targets (see fig 1).
        • Hart T.
        • Tsaousides T.
        • Zanca J.M.
        • et al.
        Toward a theory-driven classification of rehabilitation treatments.
      • Four major such *treatment groupings may be distinguished, broad classes of treatments that are similar in their essential ingredients, and that therefore (as postulated by their tripartite treatment theory) are able to act on a class of similar treatment targets
        • Hart T.
        • Tsaousides T.
        • Zanca J.M.
        • et al.
        Toward a theory-driven classification of rehabilitation treatments.
        : (1) treatments that alter the structural qualities of tissue, (2) treatments that alter or replace the functions of organs or organ systems, (3) treatments that facilitate the learning-by-doing necessary for skilled performances, and (4) treatments that facilitate the acquisition and interpretation of information in both cognitive and affective realms.
      The major treatment groupings are so defined because we expect that different classes of targets will be impacted by different types of essential ingredients (and different mechanisms of action), such that treatments within each grouping will be similar to each other and will differ from treatments found in other treatment groupings. Furthermore, we expect that defining the major treatment groupings in terms of target classes will align well with clinical decision-making, which typically begins by identifying the aspect of functioning to be changed.
      Taken together, the concepts and frames of thinking that we have developed thus far offer the prologue to a rehabilitation treatment taxonomy (RTT), rather than the taxonomy itself. A number of issues still need to be addressed before an RTT can be created and used by various stakeholder groups in their work in rehabilitation. The objective of this article is to describe some of the important challenges remaining for this effort and point at possible fruitful ways of looking for solutions, based on our preliminary explorations and, where applicable, the existing literature.

       Further Development of the Classification: Distinctions Within the Major Treatment Groupings

      A central question for the future of the RTT involves how to further subdivide the 4 groupings. As noted in Hart et al,
      • Hart T.
      • Tsaousides T.
      • Zanca J.M.
      • et al.
      Toward a theory-driven classification of rehabilitation treatments.
      the first grouping, treatments that alter the shape and size of organs or tissues, typically involve the delivery of different forms of energy. In many cases, this is mechanical energy in the form of prolonged forces that lead to tissue elongation. Other forms of energy (eg, heat) may alter the viscoelastic properties of tissues. Moreover, there may be instances where the schedule of energy delivery alters the impact on tissues, as when brief high-energy mechanical impulses lead to the tearing of tissues (eg, manipulation of a joint under anesthesia), whereas prolonged low energy impulses lead to tissue elongation. It seems likely, therefore, that treatments in this grouping can be subdivided into more specific categories that involve certain forms of energy, delivered with exact patterns, to alter particular tissues in specific ways.
      Treatments that alter organ functions typically involve delivery of some patterned input to up- or down-regulate an organ system's output, or they may be devices that substitute for a missing organ function in terms of their downstream effects. We anticipate that treatments in this group may be subdivided into more specific categories that pertain to the modality through which the organ is stimulated, and the patterning of that stimulation, because different organ systems are responsive to categorically different forms of input. Thus, for example, exposure to increasing doses of gravity may help regulate baroreceptors, exposure to certain forms of vibration or mechanical energy may regulate muscle stretch receptors, and production of specific patterns of electrical output from a cochlear implant can signal downstream acoustic processors. Further work is necessary to determine whether this approach to subdivide by input would add more than splitting according to the organs/organ systems that are changed by the treatment, which is probably a more intuitively appealing model.
      In the treatment groupings where volitional learning encompasses the mechanisms of action, further distinctions will be more complicated. Indeed, in the skilled performances category we have already attempted (and discarded) subdivisions based on (1) training in International Classification of Functioning, Disability and Health (ICF) functions versus activities, (2) implicit versus explicit learning, (3) mental versus physical skills, (4) continuous versus sequenced movement, and (5) other splits. We realized that regardless of the varied skills we considered, the same or similar active ingredients applied: various forms of coaching, instructional and motivational sets, and progression of learning demands to improve performance. The dosing parameters also involve variations in feedback, repetitions, and schedules of practice, whether the skill is mental rehearsal, manual dexterity, or widget assembly. It was only in a minority of cases that we could identify ingredients specific to a certain type of skill (eg, chaining methods for rigidly sequenced activities).
      • Hart T.
      • Tsaousides T.
      • Zanca J.M.
      • et al.
      Toward a theory-driven classification of rehabilitation treatments.
      Thus, we believe we will need some principle other than a strict Linnaean hierarchy to convey important distinctions among the many ingredients that accompany the defining one of this grouping, “facilitation of performance.” We have discussed, but not yet drafted, matrices rather than hierarchies in which to capture variations in feedback, goal setting, and other ingredients that could be active for training most skills.
      The treatment grouping concerned with supplying or modifying ideas, concepts, emotional valences, and other types of representations brings similar dilemmas for further classification. As in all the groupings, we wish to avoid specifying treatments by content, which in this case would mean the topic area of the information presented or facilitated by the therapist. This grouping, like the skilled performances grouping, consists of volitional learning processes that (as far as we know) across the board are sensitive to many of the same ingredients as the skilled performances, with no ready candidates presenting themselves for subdivision. Among the complexities of this grouping are that we lack detailed knowledge of how “internal” domains intended to be influenced by treatment (eg, thoughts and emotions) are related causally to one another and to specific ingredients (eg, various ways of presenting some piece of information, or of prompting a novel consideration of information already known).
      In this discussion and in the articles included in this supplement, it is suggested that further development of the classification is likely to take a different tack for the first 2 major treatment groupings (altering tissues and changing organ functions), which may lend themselves to orderly hierarchical subdivisions (in the style of Linnaeus), than for the latter 2 treatment groupings (facilitating learning of motor and cognitive skills, and of facts, attitudes, and values), where a more viable approach may be to organize the multiple dimensions characterizing the ingredients used by the therapist in a session or course of treatment.
      • Whyte J.
      • Dijkers M.P.
      • Hart T.
      • et al.
      Development of a theory-driven rehabilitation treatment taxonomy: conceptual issues.
      • Hart T.
      • Tsaousides T.
      • Zanca J.M.
      • et al.
      Toward a theory-driven classification of rehabilitation treatments.
      However, we must be mindful that characterizing entities within treatment groupings in very different ways raises the specter of multiple taxonomies, each with its own rules for specifying treatments, a result we would certainly prefer to avoid. Time (filled with additional work) will tell if a common structure that is simple, yet comprehensive for all treatments, may be found for the RTT as it is developed.

       What are Allowable Targets of Treatment? How Many Exist in all Rehabilitation Treatment Theories Taken Together?

      The active ingredients that facilitate learning (of whatever kind) appear to be the same or very similar across many, if not all, of the categories of skills (eg, performing ADL, use of a smart phone as a way of compensating for a weak prospective memory) and cognitive and affective schemata (eg, anatomy factoids, justifications underlying specific ways of performing ADL, or a new self-concept as a person with a disability). What is being learned is almost irrelevant—the difference between successful and unsuccessful teaching (and between a successful and an unsuccessful therapist?) is what ingredients are used in the teaching, in what combinations, when, and whether or not they are in accord with the patient's strengths, weaknesses, and personal preferences. That is, ingredients (eg, goal setting, amount and timing of feedback, chunking of information, massing vs spacing of practice) have powerful effects on learning, regardless of the topic or skill addressed. Further research on these common ingredients may reveal associations among some of them and particular domains of skill or knowledge. For example, facilitating the setting of goals based on process may be more effective for new skill development than goals based on outcome, but either type of goal might work for relearning or revising previously acquired skills. However, we doubt that these associations will ever be strong enough to make them a basis for distinguishing separate ingredients, and therefore for making a qualitative differentiation between treatment subgroups within the 2 treatment groupings based on volitional learning.
      In short, we expect there may be a stronger link between the selection of ingredients made by the clinician and how one knows or learns, rather than what one knows or becomes skilled at. In the subsequent section on bracketing, we discuss the concept of notation that would allow what is being learned to be noted for purposes of treatment description. In our conceptual scheme, we defined the target not as a particular domain of the patient's functioning, as might be indicated by making a selection from the many entries in the body functions or activities and participation taxonomies of the ICF,
      World Health Organization
      International Classification of Functioning, Disability and Health: ICF.
      but as an aspect of functioning.
      • Whyte J.
      • Dijkers M.P.
      • Hart T.
      • et al.
      Development of a theory-driven rehabilitation treatment taxonomy: conceptual issues.
      An aspect of a learned skill may be how fast the person can execute it, how likely he or she is to make errors, or how able he or she is to execute the sequence in various environments. We think it likely that such aspects are shared by skills across domains, and that their number is limited, if not in principle, then in the number that is of interest to rehabilitation professionals as they go about their daily practice. We tried to put this idea to the test by randomly selecting a few Activity entries from the ICF and having multiple people independently list what they saw as the aspects that might be the focus in rehabilitation treatment for patients with a deficit in that domain. There was much overlap between these lists, and they were short. Speed, completeness/accuracy, and a few other aspects of quality (eg, independence as judged relative to an individualized standard) were recurring terms. We believe that similar congruence exists in the aspects that would be addressed by most treatments in the cognitive/affective representation category: clinicians wish to help recipients acquire more accurate and complete knowledge, and to change their emotional reactions to facts and events, regardless of the specific content covered.
      Just the same, the issue of targets needs to be further explored. Some questions to be answered are the following:
      • What are allowable targets—that is, aspects of functioning that are legitimate concerns of rehabilitation treatment, can be defined and quantified, and around which a theory can be constructed that postulates how they might be improved? Is it even possible to predefine “allowable,” or is any aspect of functioning that is clinically relevant a potential target, as long as clinicians can find or formulate a plausible treatment theory linking the target to a set of ingredients they can deliver?
      • Do similar limitations in the number and variety of targets hold true across all 4 major treatment groupings?
      • Is there any advantage to be gained from the fact that targets in, for example, the skilled performances class of treatments may be named the same as targets in the organ function class of treatments? Are the ingredients that improve pace of heart contractions so different from treatments that improve pace of dressing that a search for common ingredients is not fruitful, and it would be more productive for clinicians and researchers to search for commonalities within the 4 major classes?
      We have also identified the problem of potential multiple targets in interventions that include extensive instructional or motivational components. For instance, a psychologist carefully explains to a patient why and how he or she should perform total body relaxation several times a day at home and at work. Doing so achieves the state of mind the patient needs to handle the stress a new job entails (subsequently discussed under the Bracketing 3 section). Should a detailed rationale for engaging in a volitional treatment be considered an active ingredient for that treatment, or a separate treatment whose target is motivation for continually engaging in the treatment selected by the therapist? Or is motivation simply part of the mechanism of action of the treatment (ie, a volitional treatment cannot have any effect unless the patient engages in it) and is it immaterial how the therapist achieves the actualization of the mechanism, much as he or she could administer heat to a muscle using either hot paraffin or infrared light? Such distinctions may appear merely semantic but represent the type of conceptual decisions that face us at every step of development of the RTT; they have significant implications for how current and future treatments are defined and classified in any classificatory system.

       Bracketing: A Tool for a More Complete Description of Interventions

      At various points in our discussions about treatments and how they might be coded in a future taxonomy, we identified situations in which it would be of value to capture information that is relevant to understanding the nature of the treatment provided, but that did not seem to be part of the treatment ingredients as defined here, and therefore did not belong in the main part of a future coding structure. In such situations, the field may adopt supplementary codes that define the treatment type (based on some aspect of the tripartite structure of theories) with bracketed codes or terms that convey other information about the treatment being provided. Several situations in which the use of brackets may be helpful are subsequently described.

       Bracketing 1: relevance of the skill and knowledge taught

      In the end, it is the skills that patients (re)learn and the knowledge they manage to acquire that constitute a major benefit of rehabilitation. However, we have chosen to focus on the active ingredients of rehabilitation interventions, and the core element is what the therapist (or nurse or physician) does for and with the patient that brings about change in the patient's functioning. Those ingredients (goal setting, repetition, feedback, etc) and their careful coordination and titration (*dosing parameters) are common across areas of functioning, whether the latter are impairments or activity limitations or participation restrictions, to use the terms of the ICF. To explain why one program is more effective than another, or one therapist is more efficient than another, reference to hours of treatment focused on a specific deficiency is not sufficient; the ingredients used need to be specified and compared in effectiveness and efficiency studies.
      This should not be understood to mean that the particular skill coached or knowledge taught is irrelevant. A person with SCI who receives exquisite teaching in everything a person with stroke needs to know is obviously ill served, as is the person with stroke who is taught everything that is of relevance to living with an SCI. The reason is that the 2 patients, when they resume their life, cannot do anything with the knowledge, whereas the right knowledge can, as postulated by enablement theory, inform many aspects of functioning through decisions made every day. The wrong knowledge may be useless, or potentially even harmful in its consequences. Thus, rehabilitation professionals, who are interested in documenting that the focus of treatment (the what) was something of relevance to the patient's documented deficits or the goal set for and with the patient on rehabilitation admission, will need to reflect the what as much as the how of the treatment session(s), the salient treatment ingredients selected. The focus group study with therapists who had completed point of care documentation for the SCI and traumatic brain injury practice-based evidence studies
      • Zanca J.M.
      • Dijkers M.P.
      Describing what we do: a qualitative study of clinicians' perspectives on classifying rehabilitation interventions.
      found that they had a strong interest in documenting not just the ingredients of treatment sessions, but additional information on the patient, the session, and its progress. (As previously indicated, a second reason for preserving information on both aspects of treatment is that there may be an interaction between ingredients, domain of treatment, and outcomes; it may be that teaching dressing is more effective with, eg, intermittent feedback, whereas teaching transfers is best done with continuous feedback. Such associations may not be a basis for differentiations between treatment ingredients or the treatment theories that specify their effects, but they may improve our theorizing, and certainly may enrich our treatment portfolios.)
      We have discussed the possibility that in a future notation system, clinicians could enter the specific skill or cognitive representation that is the focus of treatment sessions in between brackets behind the code for the active ingredient(s) (eg, 2;13.4[d540], where 2;13.4 might be the code for teaching by chaining, with intermittent feedback). The code d540 may be recognized as the ICF code for dressing, suggesting that in a treatment classification the role for the ICF taxonomies may be that of supplying the entries (and corresponding codes) for the domains of skilled performances taught. (However, see our comments on the role of the ICF, below.) Unfortunately, there is no parallel taxonomy of the cognitive and affective schemata relevant to rehabilitation, and ad hoc schemes to organize this information will need to be created, or free-text entries will need to be used.

       Bracketing 2: importance of specifying the nature of compensation

      A second application of bracketing has been discussed: brackets to specify the underlying deficit which is the reason for making a change in the patient's home or work environment, or for supplying (and providing training in the use of) a particular prosthesis or aid.
      • Whyte J.
      • Dijkers M.P.
      • Hart T.
      • et al.
      Development of a theory-driven rehabilitation treatment taxonomy: conceptual issues.
      The classification of devices, prosthetics, and orthotics is among the easiest areas in developing an RTT because they are physical entities with specific components that can be readily distinguished. In fact, there are a number of classifications of this hardware that have been developed and might be used to constitute subsections within an RTT.

      ISO. ISO/TC 168-prosthetics and orthotics. 2013. Available at: http://www.iso.org/iso/home/store/catalogue_tc/catalogue_tc_browse.htm?commid=53630. Accessed February 21, 2013.

      Chewning L, Hayward B. National classification system for assistive technology (AT): field test. Final report (revised draft). Research Triangle Park: Research Triangle Institute; 2000.

      Things become quite complicated, however, in the case of devices that compensate for underlying deficits affecting multiple activities in varied environments. A memory book, for example, may be selected because of a patient's “prospective memory impairment” but seldom compensates completely for all of the functional ramifications of that impairment. Because of this, we propose identifying the treatment target for such compensatory treatments as the activity which has been restored (eg, “timely completion of assigned tasks”), rather than the impairment that is only incompletely compensated. A strategy that is taught to compensate for all instances of impaired prospective memory (eg, periodically stopping to review one's goals and to appraise whether one is carrying them out) may also have a target of “timely completion of assigned tasks,” but its mechanism of action is very different. Subcategorization of such compensatory treatments that share such a target but have different mechanisms of action should likely make reference to the impairment(s) that the treatment bypasses because capturing this information points to distinct mechanisms of action for devices, compensatory strategies, and environmental modifications. Thus, in defining such treatments we will need a means to code the treatment itself and the impairment or activity limitation that is being addressed by its selection.
      The example of the notebook, however, raises further issues that will require more work. First is the question of how to name the treatment itself. In the aforementioned example, is the relevant descriptor “notebook,” or “organizational system with sections for appointments, tasks, and information to save,” or yet another apt label? Devices and environmental modifications, like all treatments, contain active and inactive ingredients, and it will be important to name them by the key attributes that determine their potential impact, rather than by product names or other arbitrary designations. The notebook example also challenges us to determine the level of specificity in listing the activities that are compensated, in between listing every prospective memory task individually on the one hand, and devolving to the tautological “prospective memory activities” on the other. Further examination is necessary to determine a meaningful scale of the compensation.
      Even more complex, however, is how to note the impairment or activity limitation that led to the treatment's selection. In some cases this is a single impairment and the description is rather simple, as when we provide an ankle-foot orthosis for dorsiflexor weakness. However, many cases are more fuzzy. When we provide a wheelchair to someone with lower extremity weakness, balance problems, and fatigue, for which impairment(s) are we providing it? Or are we providing it for an activity limitation (walking) and, if so, how do we decide?

       Bracketing 3: out of sight, in the mind?

      As part of a treatment program, a rehabilitation practitioner may instruct a patient in the performance of an activity that he or she is to conduct at home or in some other setting in which the practitioner is absent. The assignment of such homework has raised considerable discussion in our group, with particular controversy over what—the assignment of the homework or the performance of the homework activity itself—should be considered the treatment in this situation. In the example of a home exercise program in which a patient has been instructed to lift weights to increase muscle strength, it is the actual lifting of the weights that will influence muscle strength. However, as discussed in Hart et al,
      • Hart T.
      • Tsaousides T.
      • Zanca J.M.
      • et al.
      Toward a theory-driven classification of rehabilitation treatments.
      the therapist does not directly influence the performance of the exercise when it is done at home (as would be the case if exercise was performed in the clinic): the therapist's contribution is to select the exercise in which the patient is to be instructed, educate the patient in how to properly perform the exercise, and perhaps convey information that would motivate the patient to actually do the exercise independently.
      Thus, it is the activity selection and instruction that are the treatment in this situation, not direct facilitation of the performance of the exercise itself. In coding such a treatment, however, it is important to note in some way the nature of the exercise or activity that that patient has been instructed to perform, both because this reflects the therapist's selection of the activity and because it more fully describes the treatment interaction than would be the case if only the instructional aspects of it were coded. We expect that in most cases the activity that is being assigned as homework is also something that could be done in the clinical setting, and is likely to have its own code in the taxonomy. We propose to enter the classification of the activity that the patient is being assigned in parentheses behind the code that classifies the instructional interaction. Thus, if teaching by demonstration with corrective feedback is coded 2;14.6 and strengthening exercise is coded 3;1.2, then the code for the situation in which a therapist teaches the patient how to perform the exercise at home by demonstration with corrective feedback would be 2;14.6 (3;1.2).
      The purposes of and conventions for the 3 types of bracketing distinguished here require further study, including questions such as, at what level of detail is the bracketed material shown, and how do you specify it? The use of brackets affords opportunities for customizing use of the RTT. There may be extremes, from the therapists who want to describe the skills they taught in great detail, to the basic behavioral scientist who systematically varies ingredient admixtures from session to session or patient to patient but for whom the skills taught hardly matter.

       Role of the ICF

      A few articles have been published that used the ICF to classify treatments delivered by physical therapists.
      • Finger M.E.
      • Cieza A.
      • Stoll J.
      • Stucki G.
      • Huber E.O.
      Identification of intervention categories for physical therapy, based on the International Classification of Functioning, Disability and Health: a Delphi exercise.
      • Allet L.
      • Cieza A.
      • Burge E.
      • Finger M.
      • Stucki G.
      • Huber E.O.
      Intervention categories for physiotherapists treating patients with musculoskeletal conditions on the basis of the International Classification of Functioning, Disability and Health.
      • Burge E.
      • Cieza A.
      • Allet L.
      • Finger M.E.
      • Stucki G.
      • Huber E.O.
      Intervention categories for physiotherapists treating patients with internal medicine conditions on the basis of the International Classification of Functioning, Disability and Health.
      The reader should not be surprised to learn that we do not encourage such efforts, which essentially are a more formal extension of the goal-oriented language that we argue to be unsuitable as the basis for a rehabilitation treatment classification with solid scientific footing. The ICF categories may be useful in partially describing the target of treatment, or in identifying distal treatment aims, as discussed previously, but they do not describe what the therapist did to eliminate or reduce the deficit—the ingredients that were delivered. This practice of “naming by goal” promotes erroneous thinking by suggesting a direct and obvious relation between unnamed ingredients and targets or distal aims, where none exists.
      We previously suggested that the ICF might be used to supply codes reflecting what skilled performances are being taught, whereas an RTT would supply the codes for how that teaching is done. That does not mean that the ICF is ideal for this purpose. One of its strengths is that it is hierarchical, as a true Linnaean taxonomy: taking off footwear (d5403) is a subcategory within dressing (d540), which in turn is a subcategory of self-care (d510–d599 series), a major section within the activities and participation taxonomy (d). Thus, a clinician has an opportunity to include a broader or narrower swath of domains with a single code, depending on the need for adequately representing clinical activities for various audiences (third party payer, clinical supervisor, etc) and the portion of clinical activity to be characterized (entire course of treatment, single session, part of a session). Similarly, the needs of research, clinical service, and education may differ as to the detail level of the domain that needs to be tracked.
      However, several problems with the ICF may be identified. One easily solved is the fact that there may not be a fine enough breakdown of categories. For instance, should taking off footwear (d5403) have subcategories of shoes (d54031), slippers (d54032), and boots (d54033)? More-difficult-to-suggest subdivisions are the entries in the “interpersonal interactions” and relations categories. A therapist who has worked with a client on parenting with a disability may need a finer palette than offered by parent-child relations (d7600), but what should they be? More problematic is that in the IFC the distinction between activity limitations and participation restrictions exists on a conceptual level but is not executed at the taxonomic level. Four possible solutions are given in the ICF manual to create a separation, none of which are very satisfactory, with the result that additional efforts to make divisions have been published.
      • Whiteneck G.G.
      • Dijkers M.P.
      Difficult to measure constructs: conceptual and methodological issues concerning participation and environmental factors.
      Making this split between activity and participation may even be counterproductive from the perspective of efforts to precisely characterize treatment interventions, in that it is unlikely that participation (as that domain of functioning is conceptualized) is ever treated in itself. Rehabilitation clinicians work with patients on improving the skills and knowledge needed to participate in life situations, whether those are parenting (d7600) or political life and citizenship (d950). Improvements in participation occur because of improvements in other domains of functioning (balancing one's checkbook, ordering from a menu, operating an industrial press, etc), a phenomenon explained by enablement theory rather than treatment theory.
      A last problem for a taxonomist is that the ICF does not always consistently maintain the differentiation between body functions and activity limitations. For instance, thinking (d163) is an activity category, within the applying knowledge (d160–d179) series, but thought functions (b160) and higher-level cognitive functions (b164) are body functions, within the specific mental functions (b140–b189) subseries. In our efforts to differentiate and classify treatments, we repeatedly encountered problems along those lines. To the degree that use of a treatment taxonomy is facilitated by a presentation of domains for which a clinician can select the ingredients he or she has applied or will apply, a more useful and intuitive separation between tissues, organ functions, and skilled performances is needed than is offered by the ICF. It may be that for use in taxonomizing rehabilitation treatment sessions, an all-new classification of human functions, or a special modification of the ICF, will be needed. At the risk of reopening the debate on the relative advantages of Nagi-based versus other conceptualizations of disablement, alternative differentiations within this span of functional deficits need to be considered.
      • Marino R.J.
      Domains of outcomes in spinal cord injury for clinical trials to improve neurological function.

       Preplanned Versus Ad Hoc Rehabilitation Practitioner Behaviors

      In designing a theory-driven taxonomy, we make the assumption that ingredients are delivered in a manner that is preplanned, that the choices rehabilitation practitioners make about what ingredients to deliver is guided by a treatment theory that they have in mind before the treatment session begins. However, the practitioner's choices and behaviors are often adjusted during the treatment session in response to patient performance (eg, increasing the demands of a task as the patient demonstrates the ability to meet the initial unforeseen demands or providing different feedback to correct unforeseen errors that are observed as a task is performed). If these ad hoc adjustments are systematic, based on a theory-driven set of if-then rules about how to respond to particular aspects of the patient's performance, we still consider them to be active ingredients, even if their implementation cannot be specified in detail in advance of the session. Behavioral management interventions, for example, have underlying theories that specify exactly how ingredients are to be administered, but the implementation depends on what the patient does in a given situation.
      Many clinician behaviors in a treatment session are not preplanned or carried out with a theory-specified purpose in mind. Therapists may offer casual comments (eg, “how are you today?” or “good job”) as part of the social dynamic of their interaction with a patient. A clinician may do something to avoid patient harm or otherwise respond to a circumstance that arises (eg, providing physical assistance in response to a loss of balance to prevent a fall) without having any theory-driven motivation for that behavior. Such behaviors may be observable, responsible, and beneficial but are not considered ingredients of treatment. When applying the taxonomy to the future coding of a particular treatment interaction, we do not expect every behavior to be classifiable.
      We do not know the extent to which preplanned behaviors may be distinguished from ad hoc behaviors without some insight into what is happening in the therapist's head. Further work will likely reveal the feasibility of making this distinction based on observation alone, and whether additional feedback from the practitioner will be needed to appropriately classify treatments.

       Our Lack of Knowledge and Its Impact on Taxonomy Development

      In multiple instances, our attempts at further developing the taxonomy have been limited by the current state of scientific knowledge. Although we have certainly run into discrete examples where our taxonomy development team was lacking in knowledge of a particular area, we believe that the larger, more conceptual issue relates to constraints because of limitations in the state of the science. As noted in the literature,
      • Dijkers M.P.
      • Hart T.
      • Tsaousides T.
      • Whyte J.
      • Zanca J.M.
      Treatment taxonomy for rehabilitation: past, present, and prospects.
      • Hart T.
      • Tsaousides T.
      • Zanca J.M.
      • et al.
      Toward a theory-driven classification of rehabilitation treatments.
      • Whyte J.
      A grand unified theory of rehabilitation (we wish!). The 57th John Stanley Coulter Memorial Lecture.
      the field of rehabilitation and its associated treatments draw on a diverse array of knowledge and theories, in domains ranging from metabolic processes to wheelchair propulsion biomechanics to learning to tissue structure. Although each of these areas, along with many others relevant to rehabilitation, likely has a body of knowledge and a theory or theories that aim to explain treatments and their impact, there are often considerable limitations to the present depth of understanding. Our experience in developing the taxonomy framework and considering these issues is that in the literature describing treatments (eg, textbooks) or a single (newly proposed) treatment (more theoretical or more practical journal articles), rarely are active ingredients identified and then connected with a target through a mechanism of action. We believe this to be true even in fields where a significant amount of work has been done and in which there is thought to be considerable understanding of the nature of treatments.
      As an example, throughout our deliberations we have returned to progressive resistance exercises as a (presumably) straightforward treatment example for considering various theoretical issues. On the surface, this treatment appears very simple: muscles contracting against progressively heavier weights (active ingredient) leads to increased muscle strength (target) via muscle hypertrophy (mechanism of action). As we have considered this in more depth, however, many other considerations have come into play, raising many questions. To what degree are changes within the central nervous system responsible for observed gains in strength? Are changes in peripheral nerves part of this mechanism? To what extent? What are the influences of different types of muscle contractions (ie, concentric, eccentric, isometric)? How do we characterize increased strength in terms of muscle endurance versus power generation? What is the most appropriate way to describe the mechanism of action—identifying changes in sarcomeres, calcium release, and actin and myosin filaments? With the example of such questions spinning off the discussion of a superficially simple treatment, the reader can imagine how challenged we were to come to specific conclusions about therapies directed at aspects of self-awareness, emotional regulation, and the like. During the initial development of the conceptual framework for the taxonomy (which involved making the conceptual decisions reflected in Whyte et al
      • Whyte J.
      • Dijkers M.P.
      • Hart T.
      • et al.
      Development of a theory-driven rehabilitation treatment taxonomy: conceptual issues.
      in this supplement), in-depth consideration of examples such as this has been fruitful in helping us to develop principles for classifying treatments. In our initial attempts at further specification of treatments beyond the 4 treatment groupings currently offered,
      • Hart T.
      • Tsaousides T.
      • Zanca J.M.
      • et al.
      Toward a theory-driven classification of rehabilitation treatments.
      questions such as these have come to light, and we recognize that such considerations will be relevant to further differentiation within the 4 overarching groupings and the specification of treatments.
      We have defined the tripartite structure of treatment theories as containing reference to ingredients that act on targets via specific mechanisms of action, and we view this structure as specifying the ultimate location of a treatment in the taxonomy. Ingredients and targets are observable in principle, and are measurable. Mechanisms, on the other hand, are the typically unobserved or even unobservable processes by which ingredients cause changes in the target. Thus, mechanisms of action occupy a central place in the RTT, but they remain the most difficult to identify. The concept of mechanism of action was developed in parallel with pharmacologic depictions of the steps occurring between a patient swallowing a pill and the medication's effect somewhere in the body. (From another point of view, the mechanism of action represents the causal chain between an initial cause and its eventual effect; scientific progress consists largely of theorizing about and observing of ever more detailed causal chains, as in the search for the Higgs boson, the elementary particle of matter that was theorized to exist more than 40 years before it was found.) With respect to treatments that alter the shape or size of tissues and treatments that change organ functions, progress with respect to studying mechanisms of action may be straightforward: we can use in vitro and animal models to determine, at a rather microscopic level, what is going on. For skilled performances and cognitive and affective representations (beliefs, valences, knowledge of facts, etc), however, the neural substrate remains invisible and, even with current and future advances in imaging methods, will probably never supply an adequate level of explanation for changes in behavior. Thus, for treatments based in volitional learning, mechanisms will, for the time being, be understood as the hidden immediate consequences of clusters of ingredients with known effects on targets (eg, impact of motivational ingredients on level of effort, effects of feedback on various aspects of performance).
      • Hart T.
      • Tsaousides T.
      • Zanca J.M.
      • et al.
      Toward a theory-driven classification of rehabilitation treatments.
      As previously noted, it is not uncommon for a complete understanding of mechanisms to lag behind the ability to use empirical findings to extrapolate about the effects of ingredients. For example, people kept away from swampy areas to avoid malarial diseases for centuries before it was discovered that the disease was carried by mosquitoes that bred in swamps. Different portions of the mechanism (mosquitoes, parasites they transmit) could be discovered decades apart, and still the incremental knowledge would assist people to avoid the disease. Similarly, our knowledge of the mechanisms important to rehabilitation will accrue with every finding about the effects of specific ingredients on targets relevant to our field. We should also borrow ideas and findings about mechanisms from other fields whose aims are similar to ours. Education (instructional theory), clinical psychology, and health psychology are a few of the domains in which parallel work in identifying the best conditions and causes for positive behavior change should be tapped to assist in the search for treatment theories applicable to rehabilitation.
      Thus, rehabilitation clinicians and researchers, for the foreseeable future, will need to consider as terra incognita the mechanism of action of what often is considered the core of rehabilitation: learning and relearning skills, acquiring new knowledge, or acquiring new ways of looking at old knowledge. In practice that means that in the tripartite theory underlying these treatments, the mechanism of action shrinks into insignificance, and we have to be even more careful when we postulate or study the association between ingredients and targets. In this connection, we may refer again to the concept of the black box of rehabilitation, which has received increasing attention over the last several years.
      • DeJong G.
      • Horn S.D.
      • Conroy B.
      • Nichols D.
      • Healton E.B.
      Opening the black box of poststroke rehabilitation: stroke rehabilitation patients, processes, and outcomes.
      • Bowles K.H.
      • Martin K.S.
      • Naylor M.D.
      Using the Omaha system to describe what's inside the black box.
      • Ballinger C.
      • Ashburn A.
      • Low J.
      • Roderick P.
      Unpacking the black box of therapy – a pilot study to describe occupational therapy and physiotherapy interventions for people with stroke.
      • Bode R.K.
      • Heinemann A.W.
      • Semik P.
      • Mallinson T.
      Patterns of therapy activities across length of stay and impairment levels: peering inside the “black box” of inpatient stroke rehabilitation.
      • Conroy B.E.
      • Hatfield B.
      • Nichols D.
      Opening the black box of stroke rehabilitation with clinical practice improvement methodology.
      • Hart T.
      • Ferraro M.
      • Myers R.
      • Ellis C.A.
      Opening the black box: lessons learned from an interdisciplinary inquiry into the learning-based contents of brain injury rehabilitation.
      • Wade D.T.
      Research into the black box of rehabilitation: the risks of a type III error.
      • Whiteneck G.
      • Gassaway J.
      • Dijkers M.
      • Jha A.
      New approach to study the contents and outcomes of spinal cord injury rehabilitation: the SCIRehab Project.
      Originally, this idea referred to the fact that aside from a few generalities, we did not understand very well what happened in rehabilitation. Fifty years of research has changed much: increasing research attention has been paid to the inputs (ie, patients and their characteristics) and outputs of rehabilitation (functional, psychosocial, and quality of life outcomes), and even the ingredients get increasing attention, especially in the Practice-Based Evidence studies. However, the process of rehabilitation has largely remained a black box, which has not received the same level of attention or specification. We regard the current taxonomy effort, with its emphasis on a tripartite theory that uses mechanisms of action as the link between ingredients and targets, as addressing this issue, but we recognize that we still have the inputs of treatments (ie, ingredients) and their outputs (ie, targets) better characterized than what links them, and have effectively reduced the black box to the issue of the mechanisms of action.

       Immediate Implications of the Work to Date

      Although the development of an RTT is in the very early stages, we believe that this work can already have a positive influence on researchers and research funders. First, the distinction we highlight between treatment theory and enablement theory suggests a corresponding split in research emphasis and responsibility.
      • Whyte J.
      Contributions of treatment theory and enablement theory to rehabilitation research and practice.
      It is possible to explore enablement links among ICF variables outside the context of any specific treatment study and to begin to build and test quantitative local enablement models of human function.
      • Sullivan K.J.
      • Cen S.Y.
      Model of disablement and recovery: knowledge translation in rehabilitation research and practice.
      These models are best built by individuals with deep expertise in a given functional domain (eg, mobility, language, communication), with or without expertise in treatment. Such models would have tremendous value in guiding clinicians and clinical researchers because they would constrain predictions about distal impacts of the treatments being pursued. Other teams of researchers are likely to focus on research that tests treatment theories, by trying to clarify the mechanisms of action by which treatments exert their effects on their targets. For these researchers, our focus on treatments' active ingredients is particularly relevant in the skilled performances and cognitive and affective schemata groupings, where this work points to a need to study broad principles that affect skill or knowledge acquisition, rather than emphasizing the specific skill or knowledge to be acquired. A coherent research program in these areas may reveal the types of training ingredients that are most effective in transmitting qualitatively different kinds of skills and knowledge, and in enhancing the skills and knowledge bases of particular types of patients.
      The conceptual issues addressed in these articles are also immediately relevant to research funders and editors of academic journals. Both funders and editors can request clearer formulations of the theories that underlie researchers' proposals to develop and study treatment (grant proposals) and their reports of development and evaluation of treatment (articles). What is the actual target of the treatment and what do the researchers hypothesize as the mechanism of action? Given the mechanism and target, have they chosen an outcome measure that will plausibly respond to the treatment? Which outcome measures will respond only by enablement links, and is this the appropriate stage of research and appropriate study population in which to expect and inspect these downstream impacts?
      Those involved in the education of rehabilitation practitioners also stand to benefit from the work presented to date. Education of rehabilitation practitioners is largely learning by doing, with limited attention to theoretical underpinnings of what clinicians do—if those exist at all. Kane
      • Kane R.L.
      Improving outcomes in rehabilitation. A call to arms (and legs).
      has described this as lore heavy. We have defined a glossary of terms that may be useful to educators in defining and discussing rehabilitation treatments with their students. Our emphasis on treatment theory, and our definition of its parts (target, ingredients, mechanism of action), provides a framework for defining and explaining the underlying rationale of rehabilitation treatments, and may suggest new ways of organizing curricula based on common features of rehabilitation treatment theories. The saying that there is nothing as practical as a theory is not just tongue-in-cheek; there is truth to the claim that a theory invites one to observe reality in a new way, and systematic observation may produce new insights as to how positive change in patients might be brought about. Educators may also benefit from the availability of new research findings that arise from studies influenced by this work.
      The implications of this work for clinicians remain to be seen but are the most crucial. After all, rehabilitation research and its funding are irrelevant without actual treatments, the clinicians who administer them, and the patients who receive them. Most of the authors of this RTT conceptual framework are practicing clinicians, and to this point we have involved other clinicians in as many steps of the process as has been feasible. We are aware that to some clinicians the work presents an exciting opportunity to share ideas and to clarify what is done in day-to-day treatments, but to others it appears reductionistic in the extreme, replacing the rich biopsychosocial model and the art of therapy with a linear model that leads from ingredient to mechanism of action to target to downstream effects (aims). For the latter group it may be hard to understand why we wish to separately consider clinician behaviors that are usually enacted together in a seamless blend (eg, selecting an assistive device, training a patient in its use, and providing education about the need for assistance). Other clinicians, however, see the value in teasing out, and training new therapists in, the ingredients that differ across the 3 types of treatment included in this example: deciding on the most important features of the device to accomplish change in a specific aspect of functioning; providing instruction, practice, and coaching in effective use of the device; and prompting the patient to develop (and remember and use) a positive attitude toward applying it in the future. The tension between research perspectives that seek to break processes into their measurable component parts, and clinical perspectives that consider the process to be an irreducible healing art, is a familiar one, and is not to be avoided. Rather, we seek to create a system that will help us meet the common goal of both camps, which is to characterize and deliver the most effective treatments with which to meet the needs of the people in our care.

       Where Do We Go From Here?

      When our group started out developing an RTT, we were optimistic that in a few years' time a blueprint for such an edifice could be created and tested by building local taxonomies in disparate areas of rehabilitation (treatments for executive dysfunction and treatments for mobility interventions).
      • Hart T.
      • Tsaousides T.
      • Zanca J.M.
      • et al.
      Toward a theory-driven classification of rehabilitation treatments.
      When we rejected a version of “classification on the basis of the deficit selected for treatment” as scientifically unproductive, and we developed the concept of a tripartite theory, it became clear that these 2 presumed disparate areas are not so disparate after all, very often sharing ingredients. The implication is that an RTT, as envisioned, cannot be built piecemeal, categorizing one at a time treatments delivered by particular disciplines, or for particular diagnostic specialty areas, or particular locations or phases of rehabilitation service delivery. At least for the time being, every decision made affects how an RTT might be applied in every discipline and diagnosis and deficit; consequently, the input of clinicians, theoreticians, researchers, educators, and administrators from all disciplines will be required to create something that has short-term and long-term value for all who participate in the rehabilitation enterprise.
      Linnaeus was either brilliant or lucky when he decided to base his classification of plants on the structure of reproductive organs
      • Hoenig H.
      What would Darwin say? A historical perspective on the next steps developing a rehabilitation classification system.
      ; with minor modifications his edifice has withstood the onslaught of time, including revelations made by our ability to compare deoxyribonucleic acid of closely related and distinctly related species. However, our theorizing has led us to determine that rehabilitation interventions do not have deoxyribonucleic acid that can be used to definitely distinguish their classes, let alone other more superficial characteristics that can be used to draw hard and fast distinctions between treatment classes. Very possibly, no part of an RTT may display the beautiful hierarchical ordering that at least nonbiologists tend to imagine when they hear the word taxonomy. Instead, further development of the framework we have proposed, and the actual creation of an RTT based on that framework, will involve a messy back-and-forth between principles of theory, systematic and unsystematic observation of rehabilitation practices, and priorities of various rehabilitation stakeholders as to what organizational principles will give the best protection against the chaos that Lambe
      • Lambe P.
      Organising knowledge: taxonomies, knowledge and organisational effectiveness.
      claims is all a taxonomy entails. We invite colleagues who are not afraid to work in shifting sand, and who enjoy the challenge of creating an edifice that always will be the best possible given current knowledge and never completed (because creative clinicians and researchers will keep on creating new interventions and variations on existing interventions), to contact us. We welcome not only rehabilitation specialists, but also those active in fields such as psychotherapy, health maintenance, and research on educational methods to help us move forward through the murk of treatments that depend on long-term behavioral and affective change.
      If indeed the foundation we have created has value, it would behoove the various organizations with an interest in rehabilitation (whether that interest is primarily service delivery, professional education, research, or research funding) to develop an organizational structure that will make it possible to guide the further development and testing of the RTT in a way that benefits all, and results in an RTT that is optimized for the use of all stakeholders.

       Conclusions

      The RTT conceptual framework proposed in the other articles in this supplement offers a start for the creation of an actual taxonomy. However, a number of issues related to both the 3 key elements of the tripartite structure, and the optimal way of presenting supplemental information that may be of relevance to various classes of users, needs to be resolved before the construction of the RTT can start in earnest. Clinicians, educators, and scholars with an interest in describing what rehabilitation is treating using what specific ingredients will be challenged by the further conceptualization of the RTT framework. Broad input is needed to make the RTT something that is of value across the width of rehabilitation.

      Acknowledgments

      We thank Alexandra Voigt for creating the figure.

      Supplemental Appendix S1 Glossary of Terms

      Active ingredients – Attributes of a treatment, selected or delivered by the clinician, that play a role in the treatment's effects on the target of treatment. These include the essential ingredients associated with the treatment's known or hypothesized mechanism of action, and any other ingredients that moderate the treatment's effect(s) but may be common to multiple treatments.
      Aim(s) (of treatment) – Aspect(s) of the patient's or other recipient's functioning or personal factors that is predicted to change indirectly (via mechanisms specified in enablement/disablement theory) as a result of the treatment-induced change in the treatment target. A single treatment may have multiple aims, and there may be a chain of treatment aims (eg, exercises leading to increased strength leading to improved ambulation leading to greater community participation) with at least 1 (in the case of treatments delivered to other recipients) involving the patient's functioning. Although highly relevant to the ultimate clinical value of a treatment, these distal treatment aims are not relevant to the definition or classification of the treatment. (As previously noted, when the target of treatment is clinically and functionally significant in its own right, we avoid calling it a treatment aim to avoid confusion about direct vs indirect effects of treatment.)
      Course of treatment – Series of treatment sessions or therapist-recipient contacts that are pursuing change in a specific treatment target, sometimes with some form of treatment progression within or between contacts.
      Dosing parameters – Quantitative variations in the strength, intensity, frequency, and/or quantity of treatment ingredients; these are often expressed as an amount of time during which the recipient is continuously exposed to the ingredient, the number of times a discrete ingredient is administered, or the magnitude of the ingredient on a quantifiable scale.
      Enablement/disablement theory – Conceptual system that specifies how change in one aspect of a patient's functioning (eg, at the level of an International Classification of Functioning, Disability and Health component: body structure, body functioning, activity/activity limitation, participation/participation restriction, personal factor, or environment) will translate into changes in another aspect, specifically a characteristic classified elsewhere in the framework being used.
      Essential ingredients (of a treatment) – Active ingredients, selected or delivered by the clinician, that define a particular treatment and distinguish it from other treatments. The essential ingredients are those that are specified by the corresponding treatment theory, and are hypothesized or known to be necessary for the treatment's effects on the treatment target.
      Inactive ingredients (of a treatment) – Attributes of a treatment that do not define or moderate the impact of the treatment on the target. Ingredients may be presumed to be inactive because they are not addressed by a treatment theory (eg, the building in which the treatment is conducted) or have been empirically determined to be inactive.
      Ingredients – See Treatment ingredients
      Mechanism of action – Process by which the treatment's essential ingredients induce change in the target of treatment. A treatment theory should specify how the essential ingredients engage mechanisms of action to bring about desired treatment effects, that is, specification of the mechanism of action explains how the essential ingredients alter the treatment target within the framework of the treatment theory. Similarly, additional mechanisms of action specify how other active ingredients moderate the effects of the treatment.
      Nonvolitional treatments – Treatments whose hypothesized mechanisms of action require no effort on the part of the recipient (other than cooperation/nonresistance). Unlike volitional treatments (subsequently defined), the recipient of nonvolitional treatment is always the patient/client undergoing rehabilitation, not a third party (eg, caregiver).
      Patient/client – Person with a disability or at risk of a disability who is the intended beneficiary of treatment.
      Progression – Clinician's deliberate, systematic alteration of the treatment to maintain, over time, the degree of challenge to the body system/behavior(s) selected for change. Progression is often triggered by improvements in the target of treatment; therefore, the pace of progression (within a single treatment contact or a course of treatment) typically depends on the pace of change in the treatment target. The form that treatment progression takes (and hence the nature of the challenge that is being maintained) is often specified by the treatment theory; therefore, multiple treatment sessions may need to be observed to distinguish between one treatment and another.
      Recipient (of treatment) – Individual whose function/behavior is intended to be changed directly as a result of treatment. In most cases this is the person with a disability (patient/client recipient), but in some instances a caregiver or employer may be the other recipient who is changed by the intervention (eg, to provide care or intervention to the patient/client or to create a more supportive environment for the patient/client).
      Rehabilitation treatment taxonomy – System of classifying rehabilitation treatments based on a principle or set of principles that allows for distinctions between treatments, which have practical and/or theoretical utility.
      Session (of treatment) – Individual episode of treatment (typically minutes to a few hours), which may be repeated during a course of treatment.
      Target of treatment/treatment target – Aspect of the recipient's functioning, or personal factor, that is predicted to be directly changed by the treatment's mechanism of action. Specification of the target of treatment in a theory in terms of an International Classification of Functioning, Disability and Health variable(s) helps to define the scope of the treatment/treatment theory. (The aim of treatment refers to changes in functioning obtained in indirect ways—see Aim(s) (of treatment), above. Although there are instances where the target of treatment is functionally important in its own right, without reference to distal enablement effects, we nevertheless reserve the term treatment aim only for the functionally relevant clinical effects that are distal to the treatment target.)
      Taxonomy – System of classification or categorization based on characteristics that have important pragmatic or theoretical implications.
      Treatment – Action taken by a health professional, in the context of contact with a treatment recipient, to alter the functioning of an individual with a disability or at risk of a disability. Treatment is defined broadly to include provision of information, devices, and referrals, specific active experiences, and passive interventions.
      Treatment grouping – Broad class of treatments that is similar in essential ingredients (eg, forms of energy) and is able to act on a class of similar treatment targets (eg, tissue properties).
      Treatment ingredients – Observable (and, therefore, in principle, measurable) actions, chemicals, devices, or forms of energy that are selected or delivered by the clinician. See also Active ingredients, Dosing parameters, Essential ingredients, and Inactive ingredients.
      Treatment theory – Conceptual system that predicts the effects of specific forms of treatment on their targets, specifying the law(s) that expresses the relations between essential ingredients and treatment target changes. (This is similar to Mechanism of action but may be broader and more inclusive.)
      Volitional treatments – Treatments where a hypothesized mechanism(s) of action requires some effort on the part of the treatment recipient.

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