Minimum important differences for scales assessing symptom severity and quality of life in patients with fecal incontinence.

OBJECTIVES The objective of this study was to estimate the minimum important difference (MID) for the Fecal Incontinence Severity Index (FISI), the Colorectal-Anal Distress Inventory (CRADI) scale of the Pelvic Floor Distress Inventory, the Colorectal-Anal Impact Questionnaire (CRAIQ) scale of the Pelvic Floor Impact Questionnaire, and the Modified Manchester Health Questionnaire (MMHQ). METHODS We calculated the MIDs using anchor-based and distribution-based approaches from a multicenter prospective cohort study investigating adaptive behaviors among women receiving nonsurgical and surgical management for fecal incontinence (FI). Patient responses were primarily anchored using a Global Impression of Change scale. The MID was defined as the difference in mean change from baseline between those who indicated they were "a little better" and those who reported "no change" on the Global Impression of Change scale 3 months after treatment. The effect size and SE of measurement were the distribution methods used. RESULTS The mean changes (SD) in FISI, CRADI, CRAIQ, and MMHQ scores from baseline to 3 months after treatment were -8.8 (12.0), -52.7 (70.0), -60.6 (90.0), and -12.6 (19.2), respectively. The anchor-based MID estimates suggested by an improvement from no change to a little better were -3.6, -11.4 and -4.7, -18.1 and -8.0, and -3.2 for the FISI, CRADI (long and short version), CRAIQ (long and short version), and MMHQ, respectively. These data were supported by 2 distribution-based estimates. CONCLUSIONS The MID values for the FISI are -4, CRADI (full version, -11; short version, -5), CRAIQ (full version, -18; short version, -8), and MMHQ -3. Statistically significant improvements that meet these thresholds are likely to be clinically important.