Patient and Therapist Agreement on Performance-Rated Ability Using the de Morton Mobility Index

Objective: To determine the level of agreement between patient self-report and therapist-assessed performance of mobility using the de Morton Mobility Index (DEMMI).

Design: Interrater agreement study.

Setting: Outpatient hospital clinic.

Participants: Consecutive sample of patients (N=128) undergoing preoperative assessment for elective lower limb (LL) arthroplasty.

Interventions: Participants completed a therapist-directed assessment of the DEMMI followed by self-report of performance. A random subsample (n=62, 48%) also completed a self-report of anticipated performance before the therapist-directed assessment. Both raters (participant and therapist) were blinded to the scores obtained from the other rater.

Main outcome measures: Interrater agreement between patient self-report and therapist-directed assessment of the total DEMMI scores was assessed using the intraclass correlation coefficient model 2,1 (ICC_2,1) with a 95% confidence interval. The Bland-Altman plots were also used to illustrate the agreement between the 2 raters.

Results: The intraclass correlation coefficient (ICC) between patient self-report after performance and therapist-directed assessment of the total DEMMI score was .967 (95% confidence interval, .952-.977). The ICC between patient self-report of anticipated performance and therapist-directed assessment of the total DEMMI score was .830 (95% confidence interval, .730-.894). The Bland-Altman plots depicted higher levels of agreement among participants with impaired levels of mobility (≤74 out of 100) than did those with near-maximum DEMMI scores.

Conclusions: Patient self-report of anticipated performance is an acceptable proxy for DEMMI scores derived from the therapist rating of performance. Caution should be exercised when interpreting self-report scores of patients with near-maximum levels of mobility. Further research is required to establish whether these results can be generalized across a range of patient populations and to clinicians with differing backgrounds and expertise.