On “Test-retest reliability and minimal detectable change on balance…” Steffen T, Seney M. Phys Ther. 2008;88:733–746.

Abstract

Translating reliability coefficients into clinically meaningful representations of measurement error is a necessary and important step when the goal is to link clinical research to clinical practice. The study by Steffen and Seney1 investigates the reliability of several balance and ambulation tests and converts the obtained coefficients into minimal detectable change (MDC) estimates. The authors apply Shrout and Fleiss2 type 3,k intraclass correlation coefficients (ICC) to quantify relative reliability and, from these estimates, they calculate the standard error of measurement (SEM) to quantify measurement error in the same units as the original measurement. For some of the balance and ambulation tests, 2 trials were performed on each of 2 occasions (eg, Timed “Up & Go” Test [TUG]); for other tests (eg, Six-Minute Walk Test [6MWT]), a single measurement was performed on each of 2 occasions. In the former case, the authors reported a type 3,2 ICC; in the latter case, they presented a type 3,1 ICC. The authors’ rationale for applying the type 3,k ICC was “The ICC(3,k) was used instead of the Pearson correlation coefficient ( r ) for test-retest reliability because it assesses rating reliability by comparing the variability of different ratings of the same subject with the total variation across all ratings and all subjects.”1(pp740–741) In fact, the type 3,1 ICC provides an estimate of reliability similar to the Pearson r because neither coefficient accounts for a systematic difference in scores between the replicate measures (eg, either trials or occasions in Steffen …