Federal law prohibits discrimination in employment decisions against persons in certain protected categories. The common method for measuring discrimination involves a comparison of some aggregate statistic for protected and non-protected individuals. This approach is open to question when employment decisions are made over an extended time period. We show how to use hierarchical proportional hazards models (Cox regression models) to analyze such data. When decisions are made at one time, the proportional hazards model reduces to the familiar doubly constrained hypergeometric model.