Survival Function or Survival Curve

The survival function is a graph that shows the probability that a client "survives" in a state at least a specified time.

A survival curve shows the probability that a client "survives" in a given state for at least a specified time (or longer). Although survival curves were originally developed to study how long a patient survived symptom- or disease-free, they can also be used to study how long a client stays in a program. 

A common application is the Knowledge Bases on this web site is to study program retention. In such an application, the curve shows, for each of a number of days, the probability that the client will stay in the program that number of days or longer.