We created a binary variable representing high vs. low risk of relapse based on the diplotype of rs16969968 and rs680244 in CHRNA5 (low risk: GG_CC, GG_CT, GA_CC; high-risk: GG_TT, GA_CT, AA_ CC) and our previous findings (1). Next, we combined the genetic risks defined by CYP2A6 and CHRNA5 into a four-category variable representing the combined genetic risks from CYP2A6 and CHRNA5. We tested whether the hazard ratio for relapse associated with treatments differed across the genetic risk categories by including a product interaction term in the Cox proportional hazard regression.
