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hierarchy of evidence
“Level of evidence” is an ambiguous term, which sometimes refers to where a type of study (study design) lies in a hierarchy of evidence. Some [study designs\study design] have less risk of bias for a particular type of question. For example, randomized studies have less risk of bias than non-randomized studies for questions about treatment effects. However, there are other factors that can increase or decrease the risk of bias in both randomized and non-randomized studies. Hierarchies of evidence (based on study design) can be useful, for example, in deciding which study designs to include in a systematic review. However, they should not be confused with assessments of the risk of bias, or the certainty of the evidence, which should be assessed using explicit criteria. Because ”level of evidence” can also refer to (or be confused with) the risk of bias, or the certainty of the evidence, we recommend against using this term.
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