Introduction
Blinding is important to minimize bias in outcome assessment of clinical trials, particularly in trials with subjective outcomes.In trials with a prospective randomized open blinded endpoint (PROBE) design, patients and their proxies are aware of the treatment they received. Therefore, it may be challenging for outcome assessors to remain blinded if outcome assessment is conducted in person or by telephone (i.e. interactive outcome assessment). If assessors are able to guess the correct treatment allocation more often than expected based on chance, the assessors may have been not properly blinded.Many trials do not collect information about inadvertent unblinding by patients and proxies or by inadvertent review of other data sources, and, even if collected, trials do not report this information.