The GUI called PGA1 provides a computational and graphical interface for the relation between statistical power and sample size for dominant, co-dominant and recessive SNP or haplotype effect (Figure 1A). Since the latter approach is increasingly used, we have developed algorithms and graphical user interfaces (GUIs) to calculate the sample size and the minimum detectable relative risk in genetic case-control studies for dominant, co-dominant, and recessive models of SNPs and SNP haplotypes. Many commonly used computational tools for genetic studies are oriented towards family-based studies and only few have been developed to handle power calculations for case-control studies of single nucleotide polymorphisms (SNPs) in unrelated subjects. Yet, there is limited computer-software to assist scientists in this task. Moreover, the scientific literature describes the mathematics of power analyses for a variety of specialized experimental designs. The principals for power calculation can be found in standard statistical textbooks. Thus, it is an indispensable procedure both for a priori and a posteriori analyses in genetic association studies. Alternatively, power analysis can be used to explore possible reasons for equivocal or negative results.

Indeed, most grants applications for genetic association studies require a power analysis section to justify the research proposal. Power calculations elucidates the actual sample size needed to find a true genotype-phenotype correlation under the study constraints. Statistical power analyses constitute a key step in the design process of these studies. Case-control genetic association studies are increasingly being used in studying the genetic basis of human complex traits.

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