The current study more than tripled the sample size compared to the previous published meta-analysis on personality38, providing a substantial increase in power to detect variants. The power to detect variants that explain 0.23% of the variance (corresponding to the effect size for the most significant SNP in the previous meta-analysis38) increased from 84% to 100%. In addition, with a sample size of 63,661 individuals there is 80% power to detect variants that explain at least 0.063% of the variance in neuroticism, compared to 1.6% power given the 17,375 subjects that were included in the previous meta-analysis.38 The large increase in sample size was possible because an IRT approach enabled harmonization of personality data obtained from different personality questionnaires, which may serve as an example for gene-finding studies for other psychological, cognitive and psychiatric traits where harmonization is required to increase sample size (e.g. symptoms of depression or ADHD measured by different questionnaires).
