PREFER I was based on the German Ageing Survey (DEAS). All PREFER participants had previously participated in the German Ageing Survey and were considered eligible for the study based on inclusion criteria:
- Being 65 years or older
- Having at least two diseases from a list of diseases in DEAS
- Having declared explicit consent to participate in further studies based on DEAS
After DEAS data collection, individuals fulfilling the inclusion criteria were contacted in early 2009. The goal was to assess about 300 persons. In total, 309 participants were recruited for PREFER and were visited by trained interviewers in March 2009. Interviewers conducted a computer-assisted personal interview (CAPI), a full medication inventory and employed Peak Expiratory Flow measurements and a sit-to-stand test as indicators of physical health. In addition, participants were asked to fill in a questionnaire. In June 2009, a first postal follow-up was conducted, and in September 2009, and interviewers returned to participants in September 2009 for another personal interview and health assessments.