Correcting for the bias caused by drop-outs in hypertension trials.

A major source of bias in hypertension trials can arise from patients who are withdrawn during the course of the trial because of inadequate blood pressure control. We develop a mechanism which allows for such withdrawals while preserving the potential to make an unbiased comparison of the treatment effects. The approach is illustrated using data from a large multicentre trial of two anti-hypertensive agents in patients with mild to moderate essential hypertension.