Use the following time scale for exposure time Choose the time scale for exposure. Common time scales include: Time Scale Expressed in Days Weeks 7 Months 30.4375 Years 365.25 Exposure calculations differ depending on whether each subject experienced the event: Does the subject experience the event? Start End No reference start date ( RFSTDTC ) reference end date ( RFENDTC ) Yes reference start date ( RFSTDTC ) the earliest event start date ( AESTDTC ) To Select the Time Scale for Exposure: Specify Log Linear for Fit model type . Click the radio button corresponding to your choice.