TABLE 2.

Compilation of systematic review criteria and evidence grading standards¹

Suggested factors	Low/limited evidence	Moderate evidence	Strong evidence
Factors for assessing individual studies
Design strength and validity	Extensive limitations of the design	Minor design limitations or uncertainties	Design/implementation of high quality: feasible intervention; appropriate control group; valid duration and measurement of outcome; appropriate statistical analysis used and adequately described
Risk of bias	Substantial risk of bias	Some presence or potential for risk of bias	Methods are described in detail to disclose that bias is minimized: comparable groups are randomly generated; design includes allocation concealment and blinding; measures of compliance are included; missing data are treated appropriately; outcomes are prespecified or justified
• Selection
• Performance detection
• Attrition
• Reporting
Impact	Most studied outcomes relate to the question indirectly; effect is small, uncertain, or lacks clinical significance; low confidence that the evidence reflects the true effect, likely to change with future research	Some indirectness of outcomes; doubt about the clinical significance of the effect; moderate confidence that the evidence reflects the true effect but may be changed by further research	Outcomes (validated surrogate endpoints/biomarkers) relate directly to the research question; size of effect is clinically relevant and statistically significant; high confidence that the evidence reflects the true effect; further research very unlikely to change the estimate of effect
Generalizability	Results are likely not generalizable; narrow study population	Some doubt about generalizability	Study subjects adequately represent the population of interest
Factors considering the totality of evidence across studies
Consistency	Unexplained inconsistency among results; not similar in direction or size of effect	Minor inconsistency among results in direction and size/significance of effect or degree of association that weaken confidence in relation	Consistent findings in direction and size/significance of effect and degree of association (very minor exceptions)
Quantity	Limited number of studies and subjects (inadequate sample size)	Moderate number of studies; some variety in investigators; doubts about adequacy of sample size to avoid type I and II errors	Large number of studies and subjects (sufficient for adequate statistical power); multiple investigators

¹This table compiles systematic review elements and evaluation criteria commonly used by authoritative and policy organizations. It should be interpreted as a simplified synthesis; inquiries regarding specific organizations review framework should be directed to publicly available information referenced in Table 1.