Cross-cultural validation of the computerized animated activity questionnaire to assess activity limitations in patients with hip and knee osteoarthritis

Purpose: The computerized Animated Activity Questionnaire (AAQ) for assessing activity limitations in hip and knee osteoarthritis (HKOA) consists of video animations from which patients can choose the animation that best matches their own performance. The AAQ has demonstrated good validity and reliability. Application of the AAQ in international studies, requires good cross-cultural validity, i.e., minimal Differential Item Functioning (DIF) across countries. The aim of this study was to evaluate cross-cultural validity. Methods: Patients in 7 European countries patients completed the AAQ on a computer. Ordinal logistic regression analysis was used to evaluate DIF across languages (Dutch versus 6 other languages). DIF is defined as follows: If a patient in a country has the same level of activity limitation as a patient in the Netherlands (the reference country in which the AAQ is developed), they should score the same on each item of the AAQ. If there is a statistical significant difference between countries, there is DIF. We used frequently described criteria in literature to assess DIF between countries. Criteria for non-uniform DIF were set as a statistical significance (p <0.001) pseudo R-square change according to Nagelkerke with a magnitude larger than 0.035 between the AAQ total score and the country variable (with Dutch as the reference group). Criteria for uniform DIF were set as a statistical significant (p