Patients of the University of Wisconsin Hospital system age 65 and over made up the sample frame. Invitation letters were sent to 5,873 seniors, roughly half of whom agreed to participate. A baseline sample of 451 remained after screening. Participants answered detailed questions about their personal characteristics and their prescription drug use in the baseline survey. The researchers then constructed measures of beneficiary costs by entering this information into the Medicare Plan Finder website. Next, participants were randomly assigned to the intervention or comparison group.
The first follow-up survey was completed by 406 participants, 197 from the comparison group and 209 from the intervention group. Respondents were asked about their choice of plan for the 2007 enrollment period and their decision process. The final follow-up survey was completed by 305 participants, who were asked about their choice of plan for the 2008 enrollment period, their experience with the plan they chose during the 2007 period, and their use of prescription drugs during the period covered by the experiment. Choice of plan from the two follow-up surveys was used to determine when participants switched plans, and annual costs were computed with the Medicare Plan Finder website using reported prescription drug usage.