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Minimal Detectable Change Scores for the Wolf Motor Function Test

Arnold School of Public Health, Department of Exercise Science, Physical Therapy Program, University of South Carolina, Columbia, South Carolina, sfritz{at}mailbox.sc.edu

Sarah Blanton, DPT

School of Medicine, Department of Rehabilitation Medicine, Division of Physical Therapy, Emory University, Atlanta, Georgia

Gitendra Uswatte, PhD

Departments of Psychology and Physical Therapy, University of Alabama at Birmingham, Birmingham, Alabama

Edward Taub, PhD

Department of Psychology, University of Alabama at Birmingham, Birmingham, Alabama

Steven L. Wolf, PhD, PT

School of Medicine, Departments of Rehab Medicine, Medicine, and Cell Biology, Nell Hodgson Woodruff School of Nursing, Health and Elder Care, Emory University, Atlanta VA Rehab R&D Center, Atlanta, Georgia

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.

Key Words: Reliability • Minimal detectable change • Wolf Motor Function Test • Standard error of measure • Stroke

This version was published on September 1, 2009

Neurorehabilitation and Neural Repair, Vol. 23, No. 7, 662-667 (2009)
DOI: 10.1177/1545968309335975


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