Original research| Volume 101, ISSUE 7, P1144-1151, July 2020

Measuring Mobility in Low Functioning Hospital Patients: An AM-PAC Replenishment Project

Published:March 12, 2020DOI:


      • Few measures of function can be used longitudinally across all levels of function.
      • The Activity Measure for Post-Acute Care (AM-PAC) offers flexible administration across a broad range of function.
      • The 6-item AM-PAC Inpatient Mobility Short Form (IMSF) is widely used in hospitals.
      • Two new AM-PAC items improve measurement at very low levels of function.
      • The 8-item AM-PAC Expanded IMSF is recommended for use among patients with low function.



      To expand an existing validated measure of basic mobility (Activity Measure for Post-Acute Care [AM-PAC]) for patients at the lowest levels of function.


      Item replenishment for existing item response theory (IRT) derived measure via (1) idea generation and creation of potential new items, (2) item calibration and field testing, and (3) longitudinal pilot test.


      Two tertiary acute care hospitals.


      Consecutive inpatients (N=502) ≥18 years old, with an AM-PAC Inpatient Mobility Short Form (IMSF) raw score ≤15. For the longitudinal pilot test, 8 inpatients were evaluated.


      Fifteen new AM-PAC items were developed, 2 of which improved mobility measurement at the lower levels of functioning. Specifically, with the 2 new items, the floor effect of the AM-PAC IMSF was reduced by 19%, statistical power and measurement breadth were greater, and there was greater measurement sensitivity in longitudinal pilot testing.


      Adding 2 new items to the AM-PAC IMSF lowered the floor and increased statistical power, measurement breadth, and sensitivity.


      List of abbreviations:

      AM-PAC (Activity Measure for Post-Acute Care), CAT (computerized adaptive test), CFI (comparative fit index), DIF (differential item functioning), GPCM (generalized partial credit IRT model), ICU (intensive care unit), IMSF (Inpatient Mobility Short Form), IRT (item response theory), JHH (Johns Hopkins Hospital), NEAT (nonequivalent groups with anchor test), PROMIS (Patient-Reported Outcomes Measurement Information System), RMSEA (root mean square error of approximation), TLI (Tucker-Lewis Index), UPMC (University of Pittsburgh Medical Center)
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