Table 2Criteria for grading the quality of individual studies

RatingDescription and Criteria
  • Least risk of bias, results generally considered valid
  • Employ valid methods for selection, inclusion, and allocation of patients to treatment; report similar baseline characteristics in different treatment groups; clearly describe attrition and have low attrition; use appropriate means for preventing bias (e.g., blinding of patients, care providers, and outcomes assessors); and use appropriate analytic methods (e.g., intention-to-treat analysis)
  • Susceptible to some bias but not enough to necessarily invalidate results
  • May not meet all criteria for good quality, but no flaw is likely to cause major bias; the study may be missing information making it difficult to assess limitations and potential problems
  • Category is broad; studies with this rating will vary in strengths and weaknesses; some fair-quality studies are likely to be valid, while others may be only possibly valid
  • Significant flaws that imply biases of various kinds that may invalidate results; “fatal flaws” in design, analysis or reporting; large amounts of missing information; discrepancies in reporting; or serious problems with intervention delivery
  • Studies are at least as likely to reflect flaws in the study design or execution as the true difference between the compared interventions
  • Considered to be less reliable than higher quality studies when synthesizing the evidence, particularly if discrepancies between studies are present

From: Methods

Cover of Noninvasive Nonpharmacological Treatment for Chronic Pain: A Systematic Review Update
Noninvasive Nonpharmacological Treatment for Chronic Pain: A Systematic Review Update [Internet].
Comparative Effectiveness Review, No. 227.
Skelly AC, Chou R, Dettori JR, et al.

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