Interrater reliability of the Wolf Motor Function Test-Functional Ability Scale: why it matters

Abstract

Background: One important objective for clinical trialists in rehabilitation is determining efficacy of interventions to enhance motor behavior. In part, limitation in the precision of measurement presents a challenge. The few valid, low-cost observational tools available to assess motor behavior cannot escape the variability inherent in test administration and scoring. This is especially true when there are multiple evaluators and raters, as in the case of multisite randomized controlled trials (RCTs). One way to enhance reliability and reduce variability is to implement rigorous quality control (QC) procedures.

Objective: This article describes a systematic QC process used to refine the administration and scoring procedures for the Wolf Motor Function Test (WMFT)-Functional Ability Scale (FAS).

Methods: The QC process, a systematic focus-group collaboration, was developed and used for a phase III RCT, which enlisted multiple evaluators and an experienced WMFT-FAS rater panel.

Results: After 3 staged refinements to the administration and scoring instructions, we achieved a sufficiently high interrater reliability (weighted κ = 0.8).

Conclusions and implications: A systematic focus-group process was shown to be an effective method to improve reliability of observational assessment tools for motor behavior in neurorehabilitation. A reduction in noise-related variability in performance assessments will increase power and potentially lower the number needed to treat. Improved precision of measurement can lead to more cost-effective and efficient clinical trials. Finally, we suggest that improved precision in measures of motor behavior may provide more insight into recovery mechanisms than a single measure of movement time alone.

Keywords: assessment; impairment; motor control; observational; quality; stroke.

Figure 1

Flow diagram. The flow of data from initial administration of the WMFT by the BE to uploading of scores to the FTP site by the Rater Panel member is shown. WMFT = Wolf Motor Function Test, BE = Blinded Evaluator, FTP = File Transfer Protocol.

Figure 2

Timeline for systematic quality control process. Top – Inter-rater reliability (quadratic weighted kappa) for the WMFT-FAS Rater Panel overall for each round of analysis for each of the three rater pairs. The number of digital files (n) included in each round is listed. Bottom – Timeline of events (with dates) for the ICARE trial including revisions to the WMFT-FAS administration and scoring instructions (ASI) and other notable events before, during and after the 5 rounds of analysis. QCh = quality check conducted to ensure essential elements were met for each digital file.

Figure 3

Inter-rater reliability by task at Round 5. The quadratic weighted kappa values between members of the WMFT-FAS Rater Panel are shown for each task. The fifteen timed tasks are: 1) Forearm to table; 2) Forearm to box; 3) Extend elbow; 4) Extend elbow with weight; 5) Hand to table; 6) Hand to box; 8) Reach and retrieve; 9) Lift can; 10) Lift pencil; 11) Lift paper clip; 12) Stack checkers; 13) Flip cards; 15) Turning key in lock; 16) Fold towel; and 17) Lift basket. [Note that the two force tasks are not listed, but the full WMFT task numbering has been retained].