To evaluate the genetic correlation between smoking phenotypes and schizophrenia, five different smoking phenotypes were used (Table 1). Ever/never smoker was coded as a dichotomous phenotype, with ever smokers typically defined as having smoked 100 cigarettes lifetime (Tobacco and Genetics Consortium, 2010). Age of onset of smoking was a continuous phenotype that was log transformed for analysis, and was defined as the age of onset of regular smoking (Tobacco and Genetics Consortium, 2010). Cigarettes per day (CPD) was coded as a continuous phenotype and is correlated with nicotine dependence (Tobacco and Genetics Consortium, 2010). The phenotype of nicotine dependence was measured only among ever smokers and was defined by the Fagerström Test for Nicotine Dependence (FTND), a six item questionnaire designed to assess the intensity of physical addiction to nicotine, with scores ranging from 0 to 10 (Heatherton et al., 1991). Nicotine dependence was then classified into mild (FTND score 0–3), moderate (FTND score 4–6), or severe (FTND score 7–10), as has been done in previous research (Hancock et al., 2015). Current/former smoker was coded as a dichotomous phenotype, where
