Figure 5.

Q-Q plot for the meta-analysis of the DSPS phenotype. This quantile-quantile plot shows SNP association p values from the meta-analysis of the DSPS phenotype in the combined DSPS-case-control and Sleep Center data sets. See the first worksheet of Supplement 1 for a listing of these p values. Quantile-quantile plots can be useful in visualizing the import of SNPs associations by comparing the distributions of nominal p values with the random expectation, and they are useful in appraising possible confounding from sample stratification. The ordinate plots the observed probability (P) values on a minus LOG₁₀ scale, and the abscissa represents the expected probabilities of a random distribution on a comparable scale. The dashed red line highlights the random expectation of P statistic distributions. Pink circles highlight the two Bonferroni-significant SNPs. Note that the next 5-10 nominally-significant SNPs were sufficiently elevated above the expectation to suggest possible association.