Loss of patients in clinical trials that measure long-term survival following myocardial infarction.

Loss of patients from clinical trials can nullify adequate randomization if the loss is unequally distributed among treatment groups. This study was designed to assess the magnitude of the problem in randomized control trials evaluating long-term therapy for survivors of myocardial infarction (MI). Only 19 of 52 trials reported having an explicit policy on withdrawals in the design stage; only 2 reported blinding the decision for withdrawal and only 7 reported accounting for withdrawals in sizing. In addition, only 16 gave the reader enough information to calculate the effect of withdrawals on trial results. In 2 of these 16 trials a p less than 0.05 result obtained by including withdrawals (intention to treat method) was reduced to p less than 0.05 when withdrawals were excluded. It is evident that many long-term trials do not contain adequate data on withdrawals. Readers of published trials are seldom able to judge whether or not withdrawals might affect the final results.