A primer on survival analysis

Abstract

Survival analysis is the statistical method for studying the time between entry to a study and a subsequent event. Survival is often the most important outcome in both observational and intervention studies. The analysis of survival, however, is not simple because of a number of factors. The time between entry to a study and the end of follow-up varies during the study period, as recruitment time for each subject is different. In addition, most studies have a finite duration during which not all subjects would have experienced the outcome of interest, while some patients might leave the study or are lost to follow-up. Survival analysis is not just concerned with time from treatment to death. The outcome could be any defined event such as time to doubling of serum creatinine concentration or first rejection episode following transplantation. An understanding of the principles involved in the statistical analyses of survival is essential for critical appraisal of studies, which employ these methods, and for designing clinical studies. This brief review describes the principles of survival analysis and its application to studies in nephrology.Survival analysis is the statistical method for studying the time between entry to a study and a subsequent event. Survival is often the most important outcome in both observational and intervention studies. The analysis of survival, however, is not simple because of a number of factors. The time between entry to a study and the end of follow-up varies during the study period, as recruitment time for each subject is different. In addition, most studies have a finite duration during which not all subjects would have experienced the outcome of interest, while some patients might leave the study or are lost to follow-up. Survival analysis is not just concerned with time from treatment to death. The outcome could be any defined event such as time to doubling of serum creatinine concentration or first rejection episode following transplantation. An understanding of the principles involved in the statistical analyses of survival is essential for critical appraisal of studies, which employ these methods, and for designing clinical studies. This brief review describes the principles of survival analysis and its application to studies in nephrology.