A population-based genome-wide association (GWA) study requires thousands of cases and controls in order to detect moderate associations between SNPs and disease, and each person genotyped can cost hundreds of dollars. Thus, when researchers plan numerous GWA studies for different diseases, it would be attractive to use the same healthy control group for more than one disease if all cases are being drawn from the same underlying population. The Wellcome Trust Case Control Consortium (WTCCC) demonstrated the effectiveness of this approach by comparing case groups of 7 major diseases to a shared control group (Wellcome Trust Case Control Consortium 2007). Additionally, researchers may want to bring in publicly available controls to increase power without increasing cost. Zhuang et al. (2010) advocated this approach, and Ho and Lange (2010) did extensive simulations in this vein that demonstrate the potential improvement in power. Ho and Lange provided some examples of studies that have augmented their control groups with publicly available controls (Hom et al. 2008; Wrensch et al. 2009).
