Fit a Cox proportional hazards model to the age of onset of GAD, recognizing the right censoring and the complex sample design features of the NCS-R (stratum codes = SESTRAT, cluster codes = SECLUSTR, NCS-R part 1 sampling weight = NCSRWTSH). Consider as predictors of the hazard function the categorical age variable (AG4CAT) and the indicator variable for females (SEXF). Based on the weighted estimates of the regression parameters in this model and their estimated standard errors, is there evidence of significant differences between the age cohorts in terms of the hazard functions? What are the differences? Compute the estimated hazard ratio of initial GAD onset for females compared with males, holding age cohort constant.