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BOX 4-1

AHRQ Critical Appraisal and Grading of Evidence

Grading system used by AHRQ-Ottawa:


Basic Jadad score is assessed based on the answer to five questions listed below. Questions that are answered with a “yes” gain 1 point; questions answered with a “no” receive 0 points; the maximum score is 5. A score of 0 to 2 points is considered “low” quality, and a score of 3 to 5 points is considered “high” quality.

  1. Was the study described as random?

  2. Was the randomization scheme described and appropriate?

  3. Was the study described as double-blind?

  4. Was the method of double-blinding appropriate? (Were both the patient and the assessor appropriately blinded?)

  5. Was there a description of dropouts and withdrawals?

Grading system used by AHRQ-Tufts (based on criteria below):


A = highest quality

Studies have the least bias and results are considered valid. These studies adhere mostly to the commonly held concepts of high quality, including the following: a formal study design; clear description of the population, setting, interventions, and comparison groups; appropriate measurement of outcomes; appropriate statistical and analytical methods and reporting; no reporting errors; less than 20 percent dropout; clear reporting of dropouts; and no obvious bias. Studies must provide valid estimation of nutrient exposure from dietary assessments and/or biomarkers with reasonable ranges of measurement errors and justifications for approaches to control for confounding in their design and analyses.

B = medium quality

Studies are susceptible to some bias, but not sufficient to invalidate the results. They do not meet all the criteria in category “A”; they have some deficiencies, but none likely to cause major bias. The study may be missing information, making it difficult to assess limitations and potential problems.

C = low quality

Studies have significant bias that may invalidate the results. These studies have serious errors in design, analysis, or reporting; there are large amounts of missing information or discrepancies in reporting.

SOURCES: Jadad et al., 1996; Cranney et al., 2007; Chung et al., 2009.



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