The name "survival analysis" is slightly misleading. It is a technique for analysing "time-to-event" or "failure-time" data, which may or may not be related to survival and death in the usual sense. For brevity we will use the terms survival and death in this lecture. The value of a survival time variable must be larger than zero, i.e. a zero or a negative value is not allowed. A common problem in this type of data is censoring, meaning that the time-to-event is not observed.