Several sample selection and study duration options are available for the prospective cohort evaluation. We recommend that potential participants be randomly selected from the Social Security Administration files and the Medicare enrollment database (to ensure some representation from those eligible for Medicare due to disability) and that participants be enrolled in the study at least 1 year prior to Medicare enrollment (approximately age 64). This should ensure geographic and demographic representation across key groups and provide adequate time to collect data in advance of any Medicare enrollment decisions.
Ideally, the entire cohort will be selected at one time rather than recruiting participants on a rolling basis each year. This will shorten the overall time frame for the study and ensure that participants experience similar enrollment environments (e.g., cost of private health insurance at time of initial enrollment). To account for attrition (e.g., loss to follow-up, death), we recommend oversampling the initial cohort to ensure both that adequate data exist to answer the proposed research questions and that all participants are representative of the initial cohort.
To examine beneficiary decision-making processes adequately, we recommend the cohort study last several years, a decade or longer if possible, to ensure that beneficiaries have ample opportunity to make several plan decisions, including disenrollment. The major objectives of the study are to understand how beneficiary values and decision making change over time, and to achieve these objectives, the evaluation must extend long enough for numerous plan decisions to be made. The sample size would need to be driven by power calculations, stratification options, and funding availability.