We included studies with SNP genotypes and Fagerström Test for Nicotine Dependence (FTND) data26 collected among smokers. FTND scores range from 0 (no dependence) to 10 (highest dependence level). As before,23 we used FTND to categorize nicotine dependence as mild (scores 0–3), moderate (scores 4–6), or severe (scores 7–10). Two of the 15 studies additionally included low-intensity smokers who reported CPD as ≤10 but had no data available on the other FTND items and were defined as mildly dependent. Concordance rates between these FTND and CPD categories showed minimal phenotype misclassification (Supplementary Methods).
