RORB and bipolar disorder: While our failure to replicate the association between RORB SNPs and bipolar disorder in the trios sample could be due to the fact that case-control designs exhibit higher power than family-based designs, it also raises the possibility that our results were due to population stratification within the case-control sample, particularly as there was a higher percentage of non-Caucasians among the controls (10.6%) than among the cases (2.0%).