Censored sampling arises in a life-testing experiment whenever the experimenter does not
observe (either intentionally or unintentionally) the failure times of all units placed on a
life-test. Inference based on censored sampling has been studied during the past 50 years by
numerous authors for a wide range of lifetime distributions such as normal exponential gamma
Rayleigh Weibull extreme value log-normal inverse Gaussian logistic Laplace and Pareto.
Naturally there are many different forms of censoring that have been discussed in the
literature. In this book we consider a versatile scheme of censoring called progressive
Type-II censoring. Under this scheme of censoring from a total of n units placed on a
life-test only m are completely observed until failure. At the time of the first failure Rl
of the n - 1 surviving units are randomly withdrawn (or censored) from the life-testing
experiment. At the time of the next failure R2 of the n - 2 -Rl surviving units are censored
and so on. Finally at the time of the m-th failure all the remaining Rm = n - m -Rl - . . . -
Rm-l surviving units are censored. Note that censoring takes place here progressively in m
stages. Clearly this scheme includes as special cases the complete sample situation (when m =
nand Rl = . . . = Rm = 0) and the conventional Type-II right censoring situation (when Rl = . .
. = Rm-l = 0 and Rm = n - m).
