Development and calibration of an item bank for the assessment of activities of daily living in cardiovascular patients using Rasch analysis

BACKGROUND To develop and calibrate the activities of daily living item bank (ADLib-cardio) as a prerequisite for a Computer-adaptive test (CAT) for the assessment of ADL in patients with cardiovascular diseases (CVD). METHODS After pre-testing for relevance and comprehension a pool of 181 ADL items were answered on a five-point Likert scale by 720 CVD patients, who were recruited in fourteen German cardiac rehabilitation centers. To verify that the relationship between the items is due to one factor, a confirmatory factor analysis (CFA) was conducted. A Mokken analysis was computed to examine the double monotonicity (i.e. every item generates an equivalent order of person traits, and every person generates an equivalent order of item difficulties). Finally, a Rasch analysis based on the partial credit model was conducted to test for unidimensionality and to calibrate the item bank. RESULTS Results of CFA and Mokken analysis confirmed a one factor structure and double monotonicity. In Rasch analysis, merging response categories and removing items with misfit, differential item functioning or local response dependency reduced the ADLib-cardio to 33 items. The ADLib-cardio fitted to the Rasch model with a nonsignificant item-trait interaction (chi-square = 105.42, df = 99; p = 0.31). Person-separation reliability was 0.81 and unidimensionality could be verified. CONCLUSIONS The ADLib-cardio is the first calibrated, unidimensional item bank that allows for the assessment of ADL in rehabilitation patients with CVD. As such, it provides the basis for the development of a CAT for the assessment of ADL in patients with cardiovascular diseases. Calibrating the ADLib-cardio in other than rehabilitation cardiovascular patient settings would further increase its generalizability.