When studies are similar in design
		Meta-analysis can help you investigate the relationship between study features and study outcomes. You code the study features according to the objectives of the review. You transform the study outcomes to a common metric so that you can compare the outcomes. Last, you use statistical methods to show the relationships between study features and outcomes. from Rudner, Glass, Evartt, & Emery (2002). A user's guide to the meta-analysis of research studies