Compared with those in the lowest quartile (Q1), students in the highest quartile (Q4) for early exposure had a 73 percent increased risk of established smoking, after controlling for covariates, including early and late exposure in the same model (27.8 versus 8.6 percent; Q4 versus Q1 relative risk [RR], 1.73; 95 percent confidence interval [CI], 1.14 to 2.62).