Additionally, although these stratification analyses were applied only for meta-analyses of observational studies with categorical outcomes here, this method can refer to meta-studies with other methodological designs, such as experimentally designed studies or those including contiguous data (e.g., the meta-analysis on the association of neprilysin mRNA levels and enzyme activity with risk of AD [32], or MGMT promoter methylation levels risk with ovarian cancer [33]). Here, MGMT is linked to ovarian cancer.