simplify: a. Evidence hierarchies rank different research or evaluation study designs based on the rigour of their research methods. Evidence hierarchies vary, with different organisations using different criteria to group study designs. In general, the greater the number of high-quality studies included in the analysis and the more rigorous the research design, the higher the evidence rating. Research with the strongest indication of effectiveness, such as systematic reviews, meta-analyses and randomised controlled trials (RCTs), are usually at the top of evidence hierarchies