The aim of the study was to determine the internal consistency, test-retest reliability and measurement error of the Animated Activity Questionnaire (AAQ) for assessing activity limitations in hip and knee osteoarthritis (HKOA) patients.
A total of 1,177 patients, from six countries (the Netherlands, UK, France, Denmark, Italy and Spain), completed the AAQ, a questionnaire consisting of videos displaying 17 activities with 3-5 levels of performance, from which patients choose the video that best matches their own performance. Unidimensionality was assessed by means of confirmatory factor analysis (CFA), using the following fit indices: the Tucker-Lewis index (TFI) >0.95, comparative fit index (CFI) >0.95, and root mean square error of approximation (RMSEA) <0.06. Cronbach's alpha was computed. In 238 patients who completed the AAQ twice, the intra-class correlation coefficient (ICC) was calculated for test-retest reliability. The standard error of measurement (SEM) and the smallest detectable change (SDC) were calculated as parameters of measurement error.
The fit indices for unidimensionality were CFI 0.957, TLI 0.950, and RMSEA 0.144. Cronbach's alpha was 0.95. ICC for test-retest reliability was 0.93 (95% confidence interval 0.91 to 0.95), ranging from 0.85 to 0.98 across countries. SEM and SDC were 4.9 and 13.6, respectively, on a scale from 0 to 100, and ranging from 2.7 to 6.7, and from 7.5 to 18.4, respectively, across countries. The AAQ appeared to measure slightly more precisely in patients with knee problems and patients without prosthesis.
The AAQ seemed to be unidimensional, and showed good internal consistency and test-retest reliability. The SDC indicated that changes in scores of at least 14% indicate real improvement in activity limitations.