Tea consumption and head and neck cancer risk, overall and by sites.

Abbreviations: CI  =  confidence interval; N  =  number; 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, the year of tea drinking = 0, and the cup-year of tea drinking = 0.
c.1 cup-year  =  1 cup of tea per day ×1 year.