Joint effects of household ventilation and number of pollutant sources on lung cancer risk.

aAdjusted for age (continuous), gender, education level (illiterate/primary school/middle school/high school/college), income 10 years ago (Yuan/year, continuous), body mass index (kg/m2, continuous), family history of lung cancer (yes/no), pack-years of smoking (continuous), ethanol consumption (ml/week, continuous), and study area (Dafeng/Ganyu).bThe joint effects category for further estimation of additive interaction.cThe reference category for measures of interaction on additive scale.