Objective: To establish the internal consistency and validity of an observational method for assessing disability in mobility in patients with osteoarthritis (OA).
Methods: Data were obtained from 198 patients with OA of the hip or knee. Results of the observational method were compared with results of self-report methods (questionnaires) on disability in mobility.
Results: Both Cronbach's alpha and Mokken Scale Analysis indicate that the method is internally consistent. Using factor analysis, observed and self-reported disability in mobility were found to be closely associated and could not be differentiated.
Conclusions: The observational method is internally consistent and indeed measures disability in mobility (high convergent validity), but observations and self-report seem to yield largely equivalent information (low divergent validity). This raises questions regarding the simultaneous use of both observational and self-report methods in the assessment of disability in mobility in OA patients.