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Forestplot showing odds ratios for lung cancer comparing the fourth to the first quartile of HK:XAConditional logistic regression was performed for each cohort and was adjusted for smoking intensity using quartiles of cotinine among current smokers. Cases and controls were matched on age, sex, and smoking status. Results were combined using random effect models for each region and in all studies combined. HK:XA, 3-hydroxykynurenine:xanthurenic acid.
