We first fitted an unconditional discrete-time survival model for the occurrence of AUDs across adulthood in the probands using only the binary time-specific event indicators. The estimated hazard function captured the conditional probability that an individual would be diagnosed with an AUD in a given age interval given that he was not diagnosed in an earlier interval, and this was used to calculate the survival function over time. Figure 1 illustrates a steep decrease in survival curve of AUD occurrence in early adulthood that gradually leveled out in the 30’s and 40’s. The probability of not having an AUD through age 55 in this sample was .65. The constant baseline hazard assumption was next evaluated to assess whether the hazard rate varied significantly across adulthood. The unconditional hazard model (with time-varying hazard rates) was found to significantly improve fit compared to a model that constrained the hazard rate to equality (χ2 = 51.166, df=6, p<.001). Thus, the constant baseline hazard assumption was rejected and the hazard function was allowed to vary across age intervals in all models.
