Minimal Detectable Change Scores for the Wolf Motor Function Test

Abstract

Background. The Wolf Motor Function Test (WMFT) is an impairment-based test whose psychometrics have been examined by previous reliability and validity studies. Standards for evaluating whether a given change is meaningful, however, have not yet been addressed. Objectives. To determine the standard error of measurement (SEM) and minimal detectable change (MDC) for the WMFT. Methods. Data were collected from 6 university laboratories that participated in the EXCITE national clinical trial and included 96 individuals with sub-acute stroke (3—9 months). Measurements were made by blinded evaluators who were trained and standardized to administer the WMFT, which was completed on 2 occasions 2 weeks apart. No intervention was given between testing sessions. Results. The WMFT Performance Time score has a SEM of 0.2 seconds and a MDC95 of 0.7 seconds. The individual task timed items MDC 95 ranged from 1.0 second (turn key in lock) to 3.4 seconds (reach and retrieve) with individual task items demonstrating notablly higher variability than the average WMFT Performance Time. The average WMFT Functional Ability Scale SEM and MDC95 is 0.1 points. Conclusions. When assessing the effect of a therapeutic intervention, if an individual experiences an amount of change equal to or greater than the MDC, then one may be 95% confident that this margin of change is truly larger than measurement error and not a chance result. Thus, the determination of SEM and MDC in outcome assessments allows researchers and clinicians to distinguish which results are actual differences versus which results are simply changes resulting from error or chance.