Random assignment of proxy event dates to unexposed individuals in observational studies: An automated technique using SAS

ABSTRACT Limited technical resources are available to automate the random assignment of proxy exposure dates to unexposed populations (i.e., controls) in matched retrospective cohort studies of health services. Using disease management programs as an example, exposed and unexposed individuals have distinct eligibility dates that identify the onset of risk for exposure to the intervention. In addition to this eligibility date, exposed individuals also have unique treatment start dates. The time difference between the eligibility date and the exposure date has a frequency distribution. Based on this distribution, each unexposed individual is randomly assigned to a time difference in order to create a proxy exposure date (eligibility date + time difference=proxy exposure date). The resulting distribution of the time difference among unexposed individuals will replicate the observed distribution of the time difference of the exposed. This paper presents code to automate the random assignment of a proxy exposure date to unexposed individuals using Base SAS and SAS/STAT ®