Comparison of the item distributions for the functional difficulty and functional pain scales of the OA-FUNCTION-CAT item bank with the WOMAC physical function and pain scales. Response categories are the expected values of each category within a rating scale, calculated for each item in the scale. In contrast to item thresholds, response category expected values are provided since they more accurately express the estimated range of the item across all of its categories. (a) WOMAC physical function scale versus OA-FUNCTION-CAT functional difficulty item bank. (b) WOMAC pain scale versus OA-FUNCTION-CAT functional pain item bank. CAT, computer adaptive test; OA, osteoarthritis; WOMAC, Western Ontario and McMaster Universities Osteoarthritis Index.