The amount of heterogeneity can also be expressed using the I2 statistic.42 Other heterogeneity tests include the Sargan test,41 which can be performed using individual-level data, or a likelihood ratio test using summarized data.23 An initial visual inspection for heterogeneity is important, as a formal statistical test may have low power particularly when there are few genetic variants.43 In the example of CRP and CAD risk, the Q statistic using genome-wide significant variants from across the genome is 71.9 (16 degrees of freedom, ), indicating substantial heterogeneity. The gene discussed is CRP; the disease is coronary artery disorder.