The association between tea drinking and risk of head and neck cancer stratified by the use of alcohol, betel quid, or cigarette.

Abbreviations: CI  =  confidence interval; OR  =  odds ratio
a.OR and 95% CI were calculated using unconditional logistic regression, adjusted for sex, age, education, cigarette smoking (pack-year categories), betel quid chewing (pack-year categories), and alcohol drinking (frequency)
b.For never and occasional tea drinkers, the cup of tea per day  =  0 and the cup-year of tea = 0.
c.1 cup-year  =  1 cup of tea per day ×1 year
d.Years of consumption was cut off at the median
e.Tests for interaction were performed using only two strata (Never and former+current).