Effectiveness of blinding

Abstract

OBJECTIVE: This planned secondary analysis of the Outcomes Following Vaginal Prolapse Repairs and Midurethral Sling (OPUS) trial assessed whether treatment knowledge differed between randomized groups at 12 months and whether treatment success was affected by treatment perception. STUDY DESIGN: Sham suprapubic TVT incisions were made in masked OPUS participants randomized to no-TVT. Primary surgical outcomes and maintenance of blinding was assessed at 12 months. Knowledge of treatment assignment was compared between groups, and the relationship with treatment success rates assessed. RESULTS: Prior to the 12-month post-operative visit, only 4% (13/336) of treated participants formally reported unmasking. At 12 months, 94% (315/336) randomized participants provided treatment knowledge data. Sixteen (10%) TVT participants reported treatment knowledge; most (15, 94%) were correct; 17 (11%) of sham participants reported treatment knowledge; half (8, 47%) were correct. Similar proportions of unmasked participants who reported no treatment knowledge correctly guessed/perceived treatment assignment [sham 46 (33%) vs TVT 44 (33%)]. We did not detect significant differences in treatment success rates based on perception within and across received treatment groups [perceived sham vs. TVT overall (p=0.76)]. Of those receiving TVT, more participants perceiving TVT had treatment success compared to those that perceived sham (84% versus 74%; p=0.29). Among sham participants, more participants perceiving sham had success compared to those that perceived receiving TVT (65% vs. 56%; p= 0.42). CONCLUSION: Sham surgical incisions effectively mask TVT randomization. These findings may help to inform future surgical trial designs