Impact of unequal censoring and insufficient follow-up on comparing survival outcomes: Applications to clinical studies

Clinical trials with survival endpoints are typically designed to enroll patients for a specified number of years, (usually 2–3 years) with another specified duration of follow-up (usually 2–3 years). Under this scheme, patients who are alive or free of the event of interest at the termination of the study are censored. Consequently, a patient may be censored due to insufficient follow-up duration or due to being lost to follow-up. Potentially, this process could lead to unequal censoring in the treatment arms and lead to inaccurate and adverse conclusions about treatment effects. In this article, using extensive simulation studies, we assess the impact of such censorings on statistical procedures (the generalized logrank tests) for comparing two survival distributions and illustrate our observations by revisiting Mukherjee et al.’s1 findings of cardiovascular events in patients who took Rofecoxib (Vioxx)