Data extraction
Two authors (AP and NN) independently extracted the relevant data. The
extracted results were checked by a third author (ARP). The following
items were explored in eligible articles: author’s first name,
publication’s year, country, ethnicity, source of group, total number of
cases and controls, genotyping methods, cancer types, genotype
distribution frequencies, minor allele frequency (MAF) and P value for
Hardy-Weinberg equilibrium (HWE) in the control group. The quality of
the included studies was assessed by two authors independently according
to the modified Newcastle-Ottawa scale (NOS) (supplementary table S1).
The scores ranged from 0 (the lowest quality) to 10 points (the highest
quality) (Goto et al.). Each type of
cancer, source of control, and genotyping method with two or more
related reports were included in the subgroup analysis.