Although smoking at 14 and 31 years were collected using different questions, there was a stepwise association between the degrees of smoking severity at the two time points. Occasional-smokers at age 14, as compared to non-smokers, were almost four-times more likely to become heavy-smokers at 31 years [OR (95%CI): 4.01 (3.17–5.08), Wald-Chi-square=78.2, df=1, p<0.0001]. Regular-smokers at age 14, as compared to non-smokers, were almost ten-times more likely to become heavy-smokers at 31 years [OR (95%CI): 9.86 (7.12–13.66), Wald-Chi-square=189.3, df=1, p<0.0001]
