Deregistration after randomisation in randomized controlled trials: A systematic review

Participant deregistration after randomisation (PDAR) is an uncommon methodology used in randomised controlled trials that can negatively impact the reliability of evidence found. This is because a key feature of PDAR is that the patients deregistered are treated as though they were never randomised, and so may not be reported in the main results. As a result, true intention to treat (ITT) is compromised, and bias due to missing data cannot be readily accounted for. This review aims to identify RCTs incorporating PDAR, and evaluate reporting and implementation characteristics of PDAR across the studies identified.