Cohort

A cohort is a group of people who share a common designation, experience, or condition (e.g., Medicare beneficiaries). For the HOS, a cohort refers to a random sample of Medicare beneficiaries that is drawn from each Medicare Advantage Organization (MAO) with a minimum of 500 enrollees and surveyed every spring (i.e., a baseline survey is administered to a new cohort each year). Two years later, the baseline respondents are surveyed again (i.e., follow up measurement). For data collection years 1998-2006, the MAO sample size was 1,000. Effective 2007, the MAO sample size was increased to 1,200.