1. Amount of evidence: grade "A" is assigned when the total number of minor alleles of cases and controls combined in the meta-analyses exceeds 1,000, "B" when it is between 100 and 1,000, and "C" when it is less than 100.
2. Consistency of replication: grade "A" is assigned for I2 point estimates <25%, "B" for I2 values of 25–50%, and "C" for I2 values >50%. This criterion does not apply to meta-analyses with a P-value <1x10-7 after exclusion of the initial studie(s), as described in Khoury et al, 2009.
3. Protection from bias: the following potential reasons for bias in the meta-analysis results are systematically assessed: summary OR <1.15 ("Low OR"), loss of significance after exclusion of first study ("F"), loss of significance after exclusion of studies with deviations from Hardy-Weinberg equilibrium in control populations ("HWE"), or evidence for positive publication bias using a modified regression test ("Regr"). If none of the latter conditions are met grade "A" is assigned, otherwise grade "C".

Overall epidemiological credibility is graded as "A" (=strong) if associations received three A grades, "B" (=moderate) if they received at least one B grade but no C grades, and "C" (=weak) if they received a C grade in any of the three assessment criteria. Loci with the same grade are ordered by P-value. For more details see "Top Results Methods" and reference below.

Khoury MJ, Bertram L, Boffetta P, Butterworth AS, Chanock SJ, Dolan SM, Fortier I, Garcia-Closas M, Gwinn M, Higgins JP, Janssens AC, Ostell J, Owen RP, Pagon RA, Rebbeck TR, Rothman N, Bernstein JL, Burton PR, Campbell H, Chockalingam A, Furberg H, Little J, O'Brien TR, Seminara D, Vineis P, Winn DM, Yu W, Ioannidis JP (2009) "Genome-wide association studies, field synopses, and the development of the knowledge base on genetic variation and human diseases." Am J Epidemiol 170(3):269-79. Abstract