Introduction

Abstract

By failure time data, we mean data that concern positive random variables representing times to certain events. Examples of the event, often referred to as the failure or survival event, include death, the onset of a disease or certain milestone, the failure of a mechanical component of a machine, or learning something. The occurrence of the event is usually referred to as a failure. Sometimes we also use the terminology survival data and refer to the variable of interest as survival time or the survival variable. Failure time data arise extensively in medical studies, but there are many other investigations that also produce failure time data. These include biological studies, demographical studies, economic and financial studies, epidemiological studies, psychological experiments, reliability experiments, and sociological studies.