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Reliability of outcome measures for people with lower-limb amputations: distinguishing true change from statistical
1Providence VA Medical Center, 830 Chalkstone Ave, Providence, RI 02908, USA. Linda_Resnik@Brown.edu
Background:
Use of outcome measures to examine outcomes of amputation is complicated by a number of factors, including ease of administration and lack of scientific evidence to guide selection and interpretation.
Objective:
The purposes of this study were: (1) to estimate test-retest reliability of a modified version of the Prosthetic Evaluation Questionnaire (PEQ), scales of a version of the 36-Item Short-Form Health Survey questionnaire adapted for the veteran population (SF-36V), the Orthotics and Prosthetics Users' Survey (OPUS), the Patient-Specific Functional Scale (PSFS), the Two-Minute Walk Test, the Six-Minute Walk Test, the Timed "Up & Go" Test, and the Amputee Mobility Predictor; (2) to calculate minimal detectable change (MDC) of each measure; and (3) to conduct item analysis of the modified PEQ.
Design:
This was a multi-site study with repeated measurements.
Methods:
Forty-four patients with unilateral lower-limb amputation participated. Participants were tested twice within 1 week. We calculated test-retest reliability of each measure using intraclass correlation coefficient (ICC [2,1]), estimated standard error of the measurement and MDC, and assessed scale score distribution.
Results:
The study demonstrated strong test-retest reliability scores of performance measures (ICC=.83-.97) suggesting that these measures are good choices for evaluation of people with lower-limb amputation. Reliability of PEQ subscales (ICC=.41-.93) was comparable to that reported in the literature (ICC=.56-.90).
Limitations:
This study examined only statistically measurable differences and did not evaluate whether changes in scores were clinically important.
Conclusions:
Minimal detectable change scores can be used to determine whether change in test scores exceeds measurement error associated with day-to-day variation. This is the first study to present test-retest reliability data on the self-reported OPUS scales, the PSFS in people with lower-limb amputations, and a new, easier-to-use scoring mechanism for the PEQ.