The data assessments were carried out by the infas - Institut für angewandte Sozialwissenschaft GmbH (infas Institute for Applied Social Sciences) in Bonn in two phases:
First, an oral, face-to-face interview usually conducted in the respondent's home. These personal interviews were held by trained interviewers with a standardized questionnaire. Second, respondents were also given a questionnaire to fill out. People unable to fill out the questionnaire on their own had the opportunity of doing so with the help of the interviewer.
In the third wave of the survey the method of assessment was changed from a PAPI (Paper And Pencil Interview)-based questionnaire to a CAPI (Computer Assisted Personal Interviewing)-based approach.
During the face-to-face interview, two tests were conducted starting from 2008: the digit-symbol test assesses the participants’ “psychomotor speed”, and a peak-flow-meter is used in order to measure the respondents’ lung capacity.