Special communication| Volume 93, ISSUE 8, SUPPLEMENT , S111-S116, August 2012

Small Sample Research Designs for Evidence-Based Rehabilitation: Issues and Methods


      Graham JE, Karmarkar AM, Ottenbacher KJ. Small sample research designs for evidence-based rehabilitation: issues and methods.
      Conventional research methods, including randomized controlled trials, are powerful techniques for determining the efficacy of interventions. These designs, however, have practical limitations when applied to many rehabilitation settings and research questions. Alternative methods are available that can supplement findings from traditional research designs and improve our ability to evaluate the effectiveness of treatments for individual patients. The focus on individual patients is an important element of evidenced-based rehabilitation. This article examines one such alternate approach: small-N research designs. Small-N designs usually focus on 10 or fewer participants whose behavior (outcomes) are measured repeatedly and compared over time. The advantages and limitations of various small-N designs are described and illustrated using 3 examples from the rehabilitation literature. The challenges and opportunities of applying small-N designs to enhance evidence-based rehabilitation are discussed.

      Key Words

      List of Abbreviations:

      AFO (ankle-foot orthosis), RCT (randomized controlled trial)
      To read this article in full you will need to make a payment

      Purchase one-time access:

      Academic & Personal: 24 hour online accessCorporate R&D Professionals: 24 hour online access
      One-time access price info
      • For academic or personal research use, select 'Academic and Personal'
      • For corporate R&D use, select 'Corporate R&D Professionals'


      Subscribe to Archives of Physical Medicine and Rehabilitation
      Already a print subscriber? Claim online access
      Already an online subscriber? Sign in
      Institutional Access: Sign in to ScienceDirect


        • Law M.C.
        • MacDermid J.
        Evidence-based rehabilitation: a guide to practice.
        2nd ed. Slack, Thorofare2008
        • Kravitz R.L.
        • Duan N.
        • Braslow J.
        Evidence-based medicine, heterogeneity of treatment effects, and the trouble with averages.
        Milbank Q. 2004; 82: 661-687
        • Horn S.D.
        • DeJong G.
        • Deutscher D.
        Practice-based evidence research in rehabilitation: an alternative to randomized controlled trials and traditional observational studies.
        Arch Phys Med Rehabil. 2012; 93: S127-S137
        • Grimmer K.
        • Bialocerkowski A.
        • Kumar S.
        • Milanese S.
        Implementing evidence in clinical practice: the ‘therapies’ dilemma.
        Physiotherapy. 2004; 90: 189-194
        • Bloom M.
        • Fischer J.
        • Orme J.G.
        Evaluating practice: guidelines for the accountable professional.
        6th ed. Allyn and Bacon, Boston2009
        • Guyatt G.H.
        • Haynes R.B.
        • Jaeschke R.Z.
        • et al.
        Users' Guides to the Medical Literature: XXV.
        JAMA. 2000; 284: 1290-1296
        • Backman C.L.
        • Harris S.R.
        • Chisholm J.A.
        • Monette A.D.
        Single-subject research in rehabilitation: a review of studies using AB, withdrawal, multiple baseline, and alternating treatments designs.
        Arch Phys Med Rehabil. 1997; 78: 1145-1153
        • Johnston M.V.
        • Smith R.O.
        Single subject designs: current methodologies and future directions.
        OTJR. 2010; 30: 4-10
        • Lillie E.O.
        • Patay B.
        • Diamant J.
        • Issell B.
        • Topol E.J.
        • Schork N.J.
        The n-of-1 clinical trial: the ultimate strategy for individualizing medicine?.
        Per Med. 2011; 8: 161-173
        • Horner R.H.
        • Carr E.G.
        • Halle J.
        • McGee G.
        • Odom S.
        • Wolery M.
        The use of single-subject research to identify evidence-based practice in special education.
        Except Child. 2005; 71: 165-179
        • McDougall D.
        • Smith G.
        • Black R.
        • Rumrill P.
        Recent innovations in small-N designs for rehabilitation research: an extension of Cowan, Hennessey, Vierstra, and Rumrill.
        J Vocat Rehabil. 2005; 23: 197-205
        • Ottenbacher K.J.
        Evaluating clinical change: strategies for occupational and physical therapists.
        Williams & Wilkins, Baltimore1986
        • Gonnella C.
        Single-subject experimental paradigm as a clinical decision tool.
        Phys Ther. 1989; 69: 601-609
        • Marklund I.
        • Klassbo M.
        Effects of lower limb intensive mass practice in poststroke patients: single-subject experimental design with long-term follow-up.
        Clin Rehabil. 2006; 20: 568-576
        • Backman C.L.
        • Harris S.R.
        Case studies, single-subject research, and N of 1 randomized trials: comparisons and contrasts.
        Am J Phys Med Rehabil. 1999; 78: 170-176
        • Cowan R.J.
        • Hennessey M.L.
        • Vierstra C.V.
        • Rumrill P.D.
        Small-N designs in rehabilitation research.
        J Vocat Rehabil. 2004; 20: 203-211
        • Zhan S.
        • Ottenbacher K.J.
        Single subject research designs for disability research.
        Disabil Rehabil. 2001; 23: 1-8
        • Carey L.M.
        • Matyas T.A.
        Training of somatosensory discrimination after stroke: facilitation of stimulus generalization.
        Am J Phys Med Rehabil. 2005; 84: 428-442
        • Diamond M.F.
        • Ottenbacher K.J.
        Effect of a tone-inhibiting dynamic ankle-foot orthosis on stride characteristics of an adult with hemiparesis.
        Phys Ther. 1990; 70: 423-430
        • Harbst K.B.
        • Ottenbacher K.J.
        • Harris S.R.
        Interrater reliability of therapists' judgements of graphed data.
        Phys Ther. 1991; 71: 107-115
        • Committee on Strategies for Small-Number-Participant Clinical Research Trials
        Small clinical trials: issues and challenges.
        Institute of Medicine, National Academy Pr, Washington (DC)2001
        • Ridenour T.A.
        • Hall D.L.
        • Bost J.E.
        A small sample randomized clinical trial methodology using N-of-1 designs and mixed model analysis.
        Am J Drug Alcohol Abuse. 2009; 35: 260-266
        • Van den Noortgate W.
        • Onghena P.
        Hierarchical linear models for the quantitative integration of effect sizes in single-case research.
        Behav Res Methods Instrum Comput. 2003; 35: 1-10
        • Edington E.S.
        Randomized single-subject experimental designs.
        Behav Res Ther. 1996; 34: 567-574
        • Glass G.V.
        • Willson V.L.
        • Gottman J.M.
        Design and analysis of time-series experiments.
        Colorado Associated Univ Pr, Boulder1975
        • Harrop J.W.
        • Velicer W.F.
        A comparison of alternative approaches to the analysis of interrupted time-series.
        Multivariate Behav Res. 1985; 20: 27-44
        • Hayes S.C.
        Single case experimental design and empirical clinical practice.
        J Consult Clin Psych. 1981; 49: 193-211
        • Kazdin A.E.
        Single-case research designs in clinical child-psychiatry.
        J Am Acad Child Adolesc Psychiatry. 1983; 22: 423-432
        • Ottenbacher K.J.
        Analysis of data in idiographic research.
        Am J Phys Med Rehabil. 1992; 71: 202-208
        • Manolov R.
        • Solanas A.
        Comparing N = 1 effect size indices in presence of autocorrelation.
        Behav Modif. 2008; 32: 860-875
        • Manolov R.
        • Solanas A.
        • Leiva D.
        Comparing “visual” effect size indices for single-case designs.
        Methodology: Eur J Res Method Behav Soc Sci. 2010; 6: 49-58
        • Sackett D.L.
        • Rosenberg W.M.
        • Gray J.A.
        • Haynes R.B.
        • Richardson W.S.
        Evidence based medicine: what it is and what it isn't.
        BMJ. 1996; 312: 71-72
        • Barlow D.H.
        • Hersen M.
        Single case experimental designs: strategies for studying behavior change.
        Pergamon Pr, New York1984
        • Gabler N.B.
        • Duan N.
        • Vohra S.
        • Kravitz R.L.
        N-of-1 trials in the medical literature: a systematic review.
        Med Care. 2011; 49: 761-768
        • Koch L.C.
        • Schultz J.C.
        • Kontosh L.G.
        • Conyers L.M.
        Rehabilitation research in the 21st century: concerns and potential solutions.
        Rehabil Educ. 2006; 20: 7-19
        • Lipsey M.W.
        • Wilson D.B.
        Practical meta-analysis.
        Sage, Thousand Oaks2001
        • Johnston M.V.
        • Dijkers M.P.
        Toward improved evidence standards and methods for rehabilitation: recommendations and challenges.
        Arch Phys Med Rehabil. 2012; 93: S185-S199
        • Whyte J.
        • Barrett A.M.
        Advancing the evidence base of rehabilitation treatments: a developmental approach.
        Arch Phys Med Rehabil. 2012; 93: S101-S110

      Linked Article

      • Correction
        Archives of Physical Medicine and RehabilitationVol. 93Issue 12
        • Preview
          The article, Graham JE, Karmarkar AM, Ottenbacher KJ. Small sample research designs for evidence-based rehabilitation: issues and methods. Arch Phys Med Rehabil 2012;93:S111-6, was mistakenly published online as an uncorrected proof in May 2012. The article was embargoed to publish as a special communication with all other content for the August 2012 Archives of Physical Medicine and Rehabilitation supplemental issue (August 2012; Vol 93, No. 8, Suppl 2). In an attempt to remove the article from online publication and remedy the publishing error, the publisher erroneously retracted the article.
        • Full-Text
        • PDF