Critical appraisal
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
Why critically appraise?
• Important element of evidence based
medicine
• To weigh up how valid and useful the
research wi...
What to look for in an RCT
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
Is the methodology sound?
Publication bias in systematic
reviews
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
Papers with more “interestin...
How are the results presented?
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
• Number needed to treat (NNT)
The n...
How are the results presented?
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
• Number needed to treat (NNT)
• Odd...
Odds and risk
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
Odds of winning
1:9
You versus the rest
Risk of winni...
How are the results presented?
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
• Number needed to treat (NNT)
• Odd...
How are the results presented?
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
• Number needed to treat (NNT)
• Odd...
Forest plots
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
more than 1less than 1 1
A forest plot (or blobbogram)...
Forest plots
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
more than 1less than 1 1
Line of no effect
Anything to...
Forest plots
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
more than 1less than 1 1
Line of no effect
Best estima...
Forest plots
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
more than 1less than 1 1
Line of no effect
Best estima...
Forest plots
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
more than 1less than 1 1
Line of no effect
Best estima...
P-value
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
Could the result have occurred
by chance?
p = 0.001 (1 in 1...
How critical appraisal works
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
• Involves answering a short
questionn...
Summary
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
Validity
Is it
trustworthy?
Results
What does
it say?
Relev...
Further reading
RDF
InformationLiteracy
http://www.library.qmul.ac.uk/
Critical appraisal questionnaires / checklists
• ht...
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Critical appraisal

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Critical appraisal

  1. 1. Critical appraisal RDF InformationLiteracy http://www.library.qmul.ac.uk/
  2. 2. Why critically appraise? • Important element of evidence based medicine • To weigh up how valid and useful the research will be • Research is of variable quality • Only an estimated 1% is judged clinically relevant RDF InformationLiteracy http://www.library.qmul.ac.uk/
  3. 3. What to look for in an RCT RDF InformationLiteracy http://www.library.qmul.ac.uk/ Is the methodology sound?
  4. 4. Publication bias in systematic reviews RDF InformationLiteracy http://www.library.qmul.ac.uk/ Papers with more “interesting” results are more likely to be: • Submitted and accepted for publication • Published in a major journal • Published in English • Quoted by authors • Quoted in newspapers Have the authors addressed this in their review?
  5. 5. How are the results presented? RDF InformationLiteracy http://www.library.qmul.ac.uk/ • Number needed to treat (NNT) The number of patients that need to be treated with en intervention in order to get one additional positive outcome. E.g. if the NNT is 4, four people would need to treated with the intervention in order for one to gain benefit.
  6. 6. How are the results presented? RDF InformationLiteracy http://www.library.qmul.ac.uk/ • Number needed to treat (NNT) • Odds Ratio • Relative risk
  7. 7. Odds and risk RDF InformationLiteracy http://www.library.qmul.ac.uk/ Odds of winning 1:9 You versus the rest Risk of winning 1:10 You versus all the runners 10 horses running, you bet on 1 horse
  8. 8. How are the results presented? RDF InformationLiteracy http://www.library.qmul.ac.uk/ • Number needed to treat (NNT) • Odds Ratio • Relative risk • Mean difference This one is fairly self explanatory. It’s the difference between the mean values in the treatment group and the control group.
  9. 9. How are the results presented? RDF InformationLiteracy http://www.library.qmul.ac.uk/ • Number needed to treat (NNT) • Odds Ratio • Relative risk • Mean difference Clarity of the results is key. Are the results presented clearly?
  10. 10. Forest plots RDF InformationLiteracy http://www.library.qmul.ac.uk/ more than 1less than 1 1 A forest plot (or blobbogram) is often used in systematic reviews or meta-analyses to display data from a number of individual studies
  11. 11. Forest plots RDF InformationLiteracy http://www.library.qmul.ac.uk/ more than 1less than 1 1 Line of no effect Anything to the right of the line of no effect indicates more of the effect, anything to the left is less. If the outcome is positive you want to see more of the results on the right of the graph to show that the intervention is effective.
  12. 12. Forest plots RDF InformationLiteracy http://www.library.qmul.ac.uk/ more than 1less than 1 1 Line of no effect Best estimate Based on an average, the best estimate is the point at which the true effect of the treatment is most likely to lie
  13. 13. Forest plots RDF InformationLiteracy http://www.library.qmul.ac.uk/ more than 1less than 1 1 Line of no effect Best estimate Confidence interval Confidence intervals show the range in which the true effect of the treatment could lie. If the confidence interval crosses the line of no effect the result of the treatment is not statistically significant.
  14. 14. Forest plots RDF InformationLiteracy http://www.library.qmul.ac.uk/ more than 1less than 1 1 Line of no effect Best estimate Pooled result Confidence interval A meta-analysis will give a pooled result combining the results of the individual studies
  15. 15. P-value RDF InformationLiteracy http://www.library.qmul.ac.uk/ Could the result have occurred by chance? p = 0.001 (1 in 1000) p = 0.2 (1 in 5) A p-value of less than 0.05 (1 in 20) is considered to be statistically significant
  16. 16. How critical appraisal works RDF InformationLiteracy http://www.library.qmul.ac.uk/ • Involves answering a short questionnaire • We use the CASP questionnaires at http://www.casp-uk.net/ • Questionnaires available for different types of research
  17. 17. Summary RDF InformationLiteracy http://www.library.qmul.ac.uk/ Validity Is it trustworthy? Results What does it say? Relevance Will it help?
  18. 18. Further reading RDF InformationLiteracy http://www.library.qmul.ac.uk/ Critical appraisal questionnaires / checklists • http://www.casp-uk.net/ • http://www.cebm.net/index.aspx?o=1157 • http://www.sign.ac.uk/methodology/checklists.html General information on critical appraisal • http://www.medicine.ox.ac.uk/bandolier/painres/downloa d/whatis/what_is_critical_appraisal.pdf • http://www.nature.com/nrgastro/journal/v6/n2/full/ncpgast hep1331.html
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