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. Author manuscript; available in PMC: 2017 Dec 21.
Published in final edited form as: Annu Rev Psychol. 2015 Oct 6;67:239–261. doi: 10.1146/annurev-psych-122414-033408

Figure 2.

Figure 2

Sample size calculation as a function of power: an example calculation demonstrating the sample sizes necessary to achieve 80% power for case-control and quantitative-trait association analyses, for SNPs with MAFs of 5%, 10%, and 20% that have relative risks between 1.1 and 1.4. Calculation assumes PTSD prevalence of 15%, additive model, a type I error rate of 5 × 10−8, and perfect LD between marker and trait allele for MAF > 5%. Calculations were based on a 1:3 PTSD case-control ratio for quantitative traits such as PTSD symptoms. Abbreviations: LD, linkage disequilibrium; MAF, minor allele frequency; PTSD, posttraumatic stress disorder; QTL, quantitative trait locus; SNP, single nucleotide polymorphism; VE, environmental variance.