Manhattan (left) and quantile–quantile (QQ; right) plots of (a) fluid and (b) crystallized intelligence in the NCNG. The genomic inflation factor, based on the median χ2, as implemented in PLINK, is 1 for both fluid and crystallized intelligence. The blue line in the Manhattan plots indicates the suggestive P=1 × 10−5 threshold, whereas the red line indicates the traditional genome-wide 5 × 10−8 threshold.