↵^a Items were ranked based on the item difficulty parameter, with more difficult items on the top. The first column lists the item number as listed in the Appendix. Freq Count=number of patients who have responded to a specific item, Diff=item difficulty parameter, SE=standard error, slope=item discrimination parameter. Items 2, 11, 18, and 19 were removed from the analysis, and item 15 was split into 3 items by age group: age group 1 (age 18–44 years), age group 2 (age 45–64 years), and age group 3 (age ≥65 years). For item 15, age group 3 was dropped due to low frequency count and unstable parameter estimations.