"The basis of MAAS (the so-called A-study) is founded by a cross-sectional study involving several thousands of healthy subjects, aged 24 to 86 years at baseline. Data were collected in four consecutive panel studies. These panel studies were virtually identical with respect to structure and organization. In the first panel study A1 (1993) agroup of 2,000 subjects received an extensive postal questionnaire. Of these 2,000 subjects, 480 were actually tested at the behavioral laboratory. Three additional experiments (A2 to A4) were subsequently executed, in which some individual data were to be collected by means of postal questionnaire, and other data by in-depth neuropsychological and medical assessment, 440 to 480 subjects per panel study." Source: The Pink Book (1995).