Association tests were performed using linear or logistic association random effect models embedded in generalized estimating equations (GEE) to correct for correlations among related individuals.21 The results were unchanged when we used mixed models. Data sets containing unrelated individuals only were evaluated using linear and logistic models. Models in the German data set (PC information unavailable) were adjusted for age and sex only. Analyses were performed separately within each data set and population group, and the results were combined by meta-analysis using the inverse variance method implemented in the computer program METAL.22
