  The stratified proportional intensity model generalizes Cox's proportional
intensity model by allowing different groups of the population under study to
have distinct baseline intensity functions. In this article, we consider the
problem of estimation in this model when the variable indicating the stratum is
unobserved for some individuals in the studied sample. In this setting, we
construct nonparametric maximum likelihood estimators for the parameters of the
stratified model and we establish their consistency and asymptotic normality.
Consistent estimators for the limiting variances are also obtained.
