A substantial decrease in power is noted both with the conversion of nicotine dependence to a dichotomous CPD phenotype, and with the conversion of nicotine dependence to an ordinal FTCD variable. This loss of power is consistent across strata: within nearly every strata of gender, ethnicity, age, and comorbid diagnosis, the strongest association with rs1451240 is seen in the nicotine dependence phenotype. Indeed, tests of proportional odds for both CPD and FTCD scores indicate that there is a threshold effect (p<0.0001 in both cases). Further, varying the definitions of cases and controls does not seem to impact the results (supplemental Tables 1 and 2).
