poor clustering. Examples of QQ and cluster plots are illustrated for the Addiction study in Figure S15. Another check on the quality of top hits is to examine Manhattan signal and regional association plots of association test p-value versus chromosomal position. As noted previously [Wellcome Trust Case Control Consortium 2007], valid associations are likely to appear as a small cluster of SNPs with low p-values, unless the sentinel polymorphism is in a SNP-poor region.
