The genotypes for rs1391166 were grouped into AA (n = 31) and AT/TT (n = 81) while the genotypes for rs1497571 were grouped into CC (n = 33) and CT/TT (n = 89). This was carried out to reduce the number of statistical comparisons and to increase power to detect genotype differences by increasing cell sizes. The decision as to how to best combine the heterozygote group was based on the following steps: (1) we plotted the means of the 3 genotype groups on the dependent variables of interest and examined dominance patterns (as assumed in the power analysis described previously) to decide how to build the 2 groups and (2) if dominance patterns were not clear (the case for rs1391166) then the less frequent homozygote group was combined with the heterozygote group as is generally the case in genetic association studies.
