Survival analysis, part 1: Introduction

When time to an event (eg, how long until an event occurs?) is the main outcome of interest in a trial, the relevant data are often called survival data. The survival time for each participant is the interval from a predetermined start point, such as entry into the study, until the occurrence of the event of interest (eg, lingual retainer failure). Participants can have the same survival time, but they may have been enrolled at different calendar times. Survival analysis can be applied to various situations such as time to death from any cause after treatment for cancer, time to finish an orthodontic treatment, time to achieve initial orthodontic alignment, time to bracket failures, time to eruption of impacted canines, and so on.

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