where π0 is the prior probability that the null hypothesis is true, T is a test statistic and f0 and f1 are the probability densities of T under the null and alternative hypotheses, respectively. π0 and f1 may be unknown but could be estimated from the data [58,60,61]. Note, however, that when the true value of π0 is near one, as is likely in disease association scans, empirical estimates of π0 may be greater than one, which leads to a downward bias if these estimates are truncated at one. Thus, it is better to fix a prior estimate of π0 from genomic considerations such as the number of expected disease genes (O(101)) and the number of genes in the genome (O(104)) [62].
