This odds ratio is useful as it allows us also to estimate the size of studies needed to detect such effects and thereby assess the value of individual studies. Table 3 illustrates the total number of cases required (assuming that the total sample would in addition include an equal number of controls) in order to achieve 80% power to detect a range of effect sizes for a range of minor allele frequencies. As we can see, the majority of individual primary studies conducted are likely to be grossly under-powered to detect effect sizes of the magnitude indicated by the meta-analyses.
