0.40, respectively. Thus, the sample sizes of the current study, ~ 930 sibpairs in the AA sample, and ~ 330 sibpairs in the EA sample, should be sufficient for detecting a GRR of 1.3 for an SNP with an MAF of 0.40 for the pooled sample (~ 1260 sibpairs). It should be remembered that the case-sibling design is used as a reference for above mentioned power analyses. Because among the 402 AA families, there were 187, 199, and 16 families with 0, 1, and 2 parents, respectively (Li and others 2006), and among the 200 EA families, there were 46, 131, and 23 families with 0, 1, and 2 parents (Li and others 2008b), respectively, our study provides a greater statistical power than a pure case-sibling design. Given that rs1317286, a SNP in the CHRNA3 gene with a main effect under the dominant model in the pooled sample was included in four of the five best interaction models detected by PGMDR, and another SNP, rs3743078 in the CHRNA3 gene, without a main effect, was detected in three of the five best interaction models, power calculation with Quanto for detecting interaction between two genetic loci, g and h, was performed for
