To assess the representativeness of the sample and thus the generalizability of the future findings, four different aspects are considered:

1. Age distribution and gender: We enroll almost the same number of participants in each age group and compare the proportion in each decade of life between the participants in this study with the corresponding proportion of the general population in Germany.
2. Genetic representativeness and homogeneity: We test whether the distribution of genetic polymorphisms in the sample does not differ from the Hardy-Weinberg equilibrium (HWE).
3. Basic cognitive abilities: We test whether neuropsychological tests measuring crucial cognitive functions are comparable with reference values in the literature.
4. Education and occupation: We compare levels of education and the proportion of employed individuals in the present sample and in the general population in Germany.