Figures
Item-person map of the Urinary Incontinence Questionnaire (UIQ). The item-person map was derived by analyzing the UIQ items using Samejima's 2-parameter graded response model and Parscale. The map illustrates the relationship of the person score distribution (right) with the hierarchical order of UIQ items (left). Both person ability and item difficulty are expressed on a common metric, which is expressed along the central axis in logits, with higher positive values indicating a more difficult item or a person with a higher level of functioning.
Test information function (TIF) and standard error (SE), illustrating a bell-shaped TIF curve with one peak located at the middle ability level. The SE values were small in the middle range of patient ability measures but increased as ability measures (logits) became extreme. Overall, the TIF curve shifted slightly toward the left (lower ability measures), which implied more difficult items were needed to increase test information and thus reduce the measurement error at the high-functioning level.
Tables
Patient Characteristics at Rehabilitation Intake (N=1,628)
a HMO=health maintenance organization, PPO=preferred provider organization.
b Functional comorbidities are medical conditions shown to affect physical functioning.
Item Characteristics of the Urinary Incontinence Questionnaire (UIQ) Itemsa
↵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.
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