Table 3.

Power for Testing ER + /ER− Subgroups in Breast Cancer for 8 Known SNPs^a

SNP	Allele Frequencyb	Per-Allele Odds Ratiosc			Subtype Power, %d
		Overall	ER+ (83%)	ER− (17%)
rs2981582	0.38	1.23	1.27	1.01	90
rs3803662	0.26	1.20	1.24	1.07	92
rs13387042	0.50	1.16	1.18	1.17	92
rs889312	0.28	1.13	1.15	1.11	92
rs13281615	0.40	1.09	1.12	1.05	97
rs4666451	0.60	1.08	1.08	1.19	99
rs981782	0.54	1.06	1.05	1.12	87
rs1045485	0.87	1.05	1.04	1.16	58

Abbreviations: ER + , estrogen receptor positive; ER − , estrogen receptor negative; SNP, single nucleotype polymorphism.

^a Data adapted from Reeves et al. (14). For each row, we determine the sample size needed to achieve 90% power for detecting the “overall” relative risk in a conventional comparison of all cases versus controls.

^b Allele frequency in the control group.

^c We used the odds ratios appearing in Figure 1 of the report by Reeves et al. (14), recognizing that these are adjusted odds ratios.

^d We used the allele frequency and overall odds ratio to calculate the sample size required to deliver 90% power to detect the “overall” odds ratio in a conventional analysis of all cases versus controls using Appendix equation A2. We then used this overall sample size and equation A3 in the Appendix to calculate the power of the subtyping strategy, recognizing that “A” in the formula represents the larger of the odds ratios for ER+ and ER− in the table.