The minimum important differences for the urinary scales of the Pelvic Floor Distress Inventory and Pelvic Floor Impact Questionnaire

Objective We sought to estimate the minimum important difference (MID) for the Urinary Distress Inventory (UDI), UDI-stress subscale of the Pelvic Floor Distress Inventory, and Urinary Impact Questionnaire (UIQ) of the Pelvic Floor Impact Questionnaire. Study Design We calculated MID using anchor- and distribution-based approaches from a randomized trial for nonsurgical stress incontinence treatment. Anchors included a global impression of change, incontinence episodes from a urinary diary, and the Incontinence Severity Index. Effect size and standard error of measurement were the distribution methods used. Results Anchor-based MIDs ranged from -22.4 to -6.4 points for the UDI, -16.5 to -4.6 points for the UDI-stress, and -17.0 to -6.5 points for the UIQ. These data were supported by 2 distribution-based estimates. Conclusion Reasonable estimates of MID are 11, 8, and 16 points for the UDI, UDI-stress subscale, and UIQ, respectively. Statistically significant improvements that meet these thresholds should be considered clinically important.