Precision. A measure of the likelihood of random errors in the estimates of effect; the degree of certainty about the estimates for specific outcomes.

Quality of evidence. The extent to which one can be confident that the estimate of an intervention’s effectiveness is correct.

Reporting bias. A group of related biases that lead to overrepresentation of significant or positive studies in systematic reviews. Reporting bias includes publication bias, outcome reporting bias, time-lag bias, location bias, language bias, citation bias, and multiple- (duplicate-) publication bias.

Risk of bias. The extent to which flaws in the design and execution of a collection of studies could bias the estimate of effect for each outcome under study.

Scientific rigor. Improves objectivity, minimizes bias, provides reproducible results, and fosters more complete reporting.

Standard. A process, action, or procedure that is deemed essential to producing scientifically valid, transparent, and reproducible results. May be supported by scientific evidence, by a reasonable expectation that the standard helps achieve the anticipated level of quality, or by the broad acceptance of its practice.

Strength of association. The likelihood that a large observed effect in an observational study is not due to bias from potential confounding factors.

Study quality. For an individual study, study quality refers to all aspects of a study’s design and execution and the extent to which bias is avoided or minimized. A related concept is internal validity, that is, the degree to which the results of a study are likely to be true and free of bias.

Systematic review. A scientific investigation that focuses on a specific question and that uses explicit, planned scientific methods to identify, select, assess, and summarize the findings of similar but separate studies. It may or may not include a quantitative synthesis of the results from separate studies (meta-analysis).

Timeliness. Currency of the review.

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