GWAS of deCODE samples (8,281 ADHD cases; 137,993 controls) was done using dosage data and logistic regression with sex, year of birth, and county of origin as covariates. To account for inflation due to population stratification and cryptic relatedness, test statistics were divided by an inflation factor (lambda = 1.23) estimated from LD score regression as done previously55. Findings from analyses of the genetic structure of the Icelandic population by Price et al.73 support that lambda correction will ensure proper correction without false positives. Subsequently alleles were converted to match HRC alleles.
