Table S1.

Scale for quality assessment

Criteria	Score
Representativeness of cases
Consecutive/randomly selected form case population with clearly defined sampling frame	2
Consecutive/randomly selected form case population without clearly defined sampling frame or with extensive	1
Not described	0
Definition of the DR
Population- or health-based	2
Hospital-bases	1
Not described	0
Hardy–Weinberg equilibrium in controls
Hardy–Weinberg equilibrium	2
Hardy–Weinberg disequilibrium	1
Genotyping examination
Genotyping done under “blinded” condition	1
Unblinded done or not mentioned	0
Association assessment
Assess association between genotypes and head and neck cancer with appropriate statistics and adjustment for confounders	2
Assess association between genotypes and head and neck cancer with appropriate statistics and without adjustment for confounders	1
Inappropriate statistics used	0