`` `` two proportional hazards models for cohort fertility evaluation are constructed . time-dependent covariates describe sources of heterogeneity between and within women regarding fertility characteristics . in the first model , u.s. birth rates specific to maternal age , race , parity , and birth cohort are used as underlying hazard rates . covariate effects are estimated by maximizing the full likelihood . in the second model , covariate effects are estimated via cox regression with stratified underlying hazard rates regarded as unknown nuisance parameters . '' ''
C1521970
characteristic
C0030563
parit