Failure time regression (FTR) data are obtained by observing failure times
of units functioning under various values of explanatory variables (called also
regressors, stresses, covariables) such as temperature, voltage, load, pressure,
humidity, design, manufacture, etc. The purpose of the FTR data analysis is
to estimate reliability under specified values of interest of these variables. In
the particular case of accelerated life testing (ALT) data are collected from
experiments under higher than usual stress conditions and reliability under
usual (design) stress is estimated.
Models relating reliability characteristics to explanatory variables are called
failure time regression models. In ALT such models are called accelerated life
models.
Degradation data with explanatory variables are obtained when failure times
and quantities characterizing degradation of units under explanatory variables
are measured. Models relating degradation to explanatory variables and models
relating intensity of failures to degradation and to these variables are used
for analysis of such data.