Guidelines:
The Meta-analysis Of Observational Studies in Epidemiology (MOOSE) guidelines can be used to critically appraise published meta-analyses that include observational studies only. Observational studies are defined as an etiology or effectiveness studies that use data from an existing database, a cross-sectional study, a case series design, a case-control design, a design with historical controls, or a cohort design. Meta-analyses using observational studies are controversial because of inherent bias and differences in study designs. However, this type of meta-analysis is steadily increasing in the published literature and having these guidelines will help you with your critical appraisal.