Table 3. Individual and joint effects of smoking and drinking on oral and oropharyngeal cancer adjusted for gender, age, schooling level.

Category	Model-1 OR (95% CI)	Model-2 OR (95% CI)
Exposures dichotomously classifieda
Ever smoker	3.50 (2.76–4.44)	1.41 (1.02–1.96)
Ever drinker	3.60 (2.86–4.53)	0.78 (0.48–1.27)
Ever smoker and ever drinker	12.60 (7.89–20.13)	8.16 (2.09–31.78)
Exposures classified in three categoriesb
Never smoker and never drinker	1.00	1.00
Never smoker and level-1 drinker	1.68 (1.29–2.20)	0.63 (0.40–1.00)
Never smoker and level-2 drinker	5.71 (4.41–7.39)	1.51 (0.88–2.57)
Level-1 smoker and never drinker	2.06 (1.57–2.70)	1.17 (0.80–1.71)
Level-1 smoker and level-1 drinker	3.47 (2.03–5.94)	2.42 (0.57–10.30)
Level-1 smoker and level-2 drinker	11.78 (6.94–19.97)	8.61 (2.05–36.13)
Level-2 smoker and never drinker	4.61 (3.53–6.01)	2.05 (1.39–3.03)
Level-2 smoker and level-1 drinker	7.76 (4.56–13.21)	6.32 (1.61–24.83)
Level-2 smoker and level-2 drinker	26.32 (15.59–44.42)	19.10 (3.85–94.72)

Model-1 did not account for the smoking-drinking interaction, smoking and drinking were therefore treated only as confounders. Model-2 accounted for the smoking-drinking interaction.

^aModel-1: Pseudo-R² = 0.118; −2log likelihood = 3346.826. Model-2: Pseudo-R² = 0.134; −2log likelihood = 3285.967.

Difference in goodness of fit between Model-1 and Model-2: likelihood ratio test χ² = 60.859, p<0.001.

^bModel-1: Pseudo-R² = 0.175; −2log likelihood = 3130.079. Model-2: Pseudo-R² = 0.186; −2log likelihood = 3088.889.

Difference in goodness of fit between Model-1 and Model-2: likelihood ratio test χ² = 41.190, p<0.001.