We used five study samples that collected FTND data from 1989 to 2013: African American Nicotine Dependence (AAND), Collaborative Genetic Study of Nicotine Dependence (COGEND), Center for Oral Health Research in Appalachia (COHRA1), Chronic Obstructive Pulmonary Disease Gene (COPDGene®), and University of Wisconsin Transdisciplinary Tobacco Use Research Center (UW-TTURC). See Supplementary Material and Table S11 for detailed sample descriptions. All protocols received Institutional Review Board approval at their respective sites. All study participants provided informed consent.
