The Fecal Incontinence Quality of Life Scale (FIQL) : improving outcomes measurement

The Fecal Incontinence Quality of Life scale (FIQL) is a patient reported outcome measure (PROM) that is used to measure the effect that fecal incontinence has on quality of life, and has previously demonstrated high reliability and validity. It measures four domains of quality of life: lifestyle, coping/behavior, depression/self-perception, and embarrassment. Despite its wide use, previous studies have not applied rigorous modern methods to evaluate the FIQL's psychometric properties at the item and test level. This thesis used a cohort of prospectively recruited patients from an elective surgical registry and applied methods from classical test theory (CTT), exploratory factor analysis (EFA), item response theory (IRT), and differential item and test functioning (DIF) to identify strengths and weaknesses in the FIQL. Specifically, this thesis aims to 1) confirm the reliability of the instrument, 2) describe the domains of quality of life measured by the instrument, 3) identify high and low quality items, and 4) determine whether one's score on the FIQL is influenced by gender or surgical procedure. Out of 317 completed questionnaires from 880 total eligible patients, 236 were included for analysis. Reliability for all four domains was high as measured by Cronbach's α. Exploratory factor analysis failed to identify the four domains the FIQL claims to measure. Individual items demonstrated high discrimination but most had low difficulty. Items 2c, 2l, 3a, and 3h failed to demonstrate good separation between response categories. Five item pairs demonstrated local item dependence, most from question 3. Only item 2g demonstrated differential item functioning, based on gender. Differential test functioning was minimal. The FIQL demonstrated a high degree of reliability, and the lifestyle domain can be used as is or with minor improvements. The FIQL can be improved by making response options consistent, distributing items from different domains evenly throughout the instrument, adding items with higher difficulty and better response separation, and removing items 2c, 2l, 3a, and 3h. Further research is needed before the FIQL can be used confidently as a stand-alone measure of fecal incontinence-related quality of life.Medicine, Faculty ofPopulation and Public Health (SPPH), School ofGraduat