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Systematic Review Service: Critical Appraisal of Studies

Appraising the Evidence

Evaluating the quality of evidence for outcomes reported in systematic reviews involves consideration of within-study risk of bias (methodological quality), directness of evidence, heterogeneity, precision of effect estimates and risk of publication bias. (Cochrane Handbook

There are numerous systems for rating evidence. Presented on this page are just a few useful resources for assessing the studies identified during your systematic search.

Center for Evidence Based Medicine

The Centre for Evidence Based Medicine (CEBM) provides useful tools and worksheets for the critical appraisal of medical evidence. Example appraisal sheets are provided along with downloadable calculators and CEBM's critical appraisal software tool, CATmaker.

Find critical appraisal sheets, calculators and more here. 

CASP (Critical Appraisal Skills Programme)

CASP International Network has developed a variety of tools to assist with appraising published research. Tools are available for appraising randomized controlled trials, qualitative research studies, systematic reviews and more.


JBI's critical appraisal tools assist in assessing the trustworthiness of published research. 

University of South Australia

The International Centre for Allied Health Evidence provides an extensive list of critical appraisal tools as well as guidance on building your own tool.

The GRADE Approach

The Grades of Recommendation, Assessment, Development and Evaluation Working Group (GRADE Working Grouphas developed a system for grading the quality of evidence.  Over 20 organizations including the World Health Organization (WHO), the American College of Physicians, the American College of Chest Physicians (ACCP), BMJ Clinical Evidence, the National Institute for Health and Clinical Excellence (NICE) in the UK and UpToDate® have adopted the GRADE system.  

The Cochrane Collaboration has adopted the principles of the GRADE system for evaluating the quality of evidence for outcomes reported in systematic reviews. 

The GRADE approach specifies four levels of quality. For detailed guidance on using the GRADE system, see the Cochrane Handbook, section 12.2.1.


The QUADAS tool was developed to evaluate the risk of bias and applicability of primary diagnostic accuracy studies.  It was first published in 2003 through a collaborative project between  the Centre for Reviews and Dissemination, University of York, and the Academic Medical Centre at the University of Amsterdam.  The current version, QUADAS-2, is structured around four key domains:

  • patient selection
  • index test
  • reference standard
  • flow and timing

QUADAS has been recommended by AHRQ and NICE.  The Cochrane Collaboration's Diagnostic Test Accuracy Working Group recommends a tool derived from the QUADAS instrument.