Table 1.

Characteristics of included studies on oral cancer.

Authors	Year	Location	Study type	Sample Size  (cases/controls)  (Cohort size/oral cancer cases)∗∗	Quality assessment∗	Mean age of cases	Adjustment for smoking and alcohol
Sankaranarayanan et al. [29]	1989	India	Case-control	228/453	Moderate	n/a	Smoking and alcohol
Sankaranarayanan et al. [30]	1989	India	Case-control	187/895	Moderate	n/a	Smoking and alcohol
Goud et al. [32]	1990	India	Case-control	102/102	Weak	53	No
Nandakumar et al. [33]	1990	India	Case-control	348/348	Moderate	54.8	No
Sankaranarayanan et al. [31]	1990	India	Case-control	414/895	Moderate	n/a	Smoking and alcohol
Rao et al. [34]	1994	India	Case-control	713/635	Moderate	50.35	Smoking and alcohol
Khan et al. [35]	1995	Pakistan	Case-control	24/24	Moderate	54	No
Wasnik et al. [36]	1998	India	Case-control	123/246	Moderate	n/a	No
Dikshit and Kanhere [37]	2000	India	Case-control	558/260	Moderate	n/a	Smoking
Merchant et al. [38]	2000	Pakistan	Case-control	79/149	Moderate	49	Smoking and alcohol
Balaram et al. [39]	2002	India	Case-control	591/582	Moderate	n/a	No
Znaor et al. [40]	2003	India	Case-control	1563/3638	Moderate	n/a	Smoking and alcohol
Subapriya et al. [41]	2007	India	Case-control	388/388	Moderate	50.85	No
Gangane et al. [42]	2007	India	Case-control	140/380	Weak	n/a	No
Basu et al. [43]	2008	India	Case-control	110/110	Weak	n/a	No
Muwonge et al. [44]	2008	India	Case-control	282/1410	Moderate	n/a	Smoking and alcohol
Jayalekshmi et al. [45]	2009	India	Cohort study	79593/92∗∗	Moderate	n/a	No
Jayalekshmi et al. [46]	2011	India	Cohort study	66277/160∗∗	Moderate	n/a	No
Pednekar et al. [47]	2011	India	Cohort study	87222/1267∗∗	Moderate	n/a	No
Madani et al. [48]	2012	India	Case-control	350/350	Moderate	n/a	Smoking and alcohol
Ray et al. [49]	2013	India	Case-control	698/948	Weak	n/a	No

∗Based on the “Effective Public Health Project Quality Assessment Tool for Quantitative Studies”.

∗∗Size of the cohort and the number of oral cancer cases in the cohort.