Cox, D. R. (1972). Regression models and life‐tables. Journal 
of the Royal Statistical Society: Series B (Methodological), 
34(2), 187-202.

Abstract
The analysis of censored failure times is considered. It is 
assumed that on each individual are available values of one or 
more explanatory variables. The hazard function (age-specific 
failure rate) is taken to be a function of the explanatory variables 
and unknown regression coefficients multiplied by an arbitrary and 
unknown function of time. A conditional likelihood is obtained, 
leading to inferences about the unknown regression coefficients. 
Some generalizations are outlined.