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Literature Appraisal Effectiveness of Therapy

Literature Appraisal Effectiveness of Therapy. Measures of treatment effect. Statistical significance Odds ratio Relative risk Absolute risk reduction Number needed to treat. Measures of treatment effect. Outcome (death) Yes No Control a b Experiment c d. Total. 200.

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Literature Appraisal Effectiveness of Therapy

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  1. Literature AppraisalEffectiveness of Therapy

  2. Measures of treatment effect • Statistical significance • Odds ratio • Relative risk • Absolute risk reduction • Number needed to treat

  3. Measures of treatment effect Outcome (death) Yes No Control a b Experiment c d

  4. Total 200

  5. Total in each group 100 200 100

  6. After 1 year Total in each group Die 25 100 200 10 100

  7. After 1 year Total in each group Die (Survive) 100 25 + (75) 200 100 10 + (90)

  8. Risk & Relative Risk

  9. After 1 year What is the Total in each group Die (Survive) Risk? (a proportion) 100 25 + (75) 200 100 10 + (90)

  10. After 1 year Total in each group Die (Survive) Risk 100 25 + (75) 200 100 10 + (90)

  11. After 1 year Total in each group Die (Survive) Risk 100 25 + (75) 200 100 10 + (90)

  12. After 1 year Total in each group Die (Survive) Risk 100 25 + (75) 200 100 10 + (90)

  13. After 1 year Die (Survive) Risk 100 25 + (75) 0.2525% 200 100 10 + (90)

  14. After 1 year Die (Survive) Risk 100 25 + (75) 0.25 25% 200 100 10 + (90)

  15. Die (Survive) Risk 100 25 + (75) 0.25 25% 200 0.110% 100 10 + (90)

  16. Die (Survive) Risk 100 25 + (75) 0.25 25% 200 100 10 + (90) 0.1 10%

  17. Die (Survive) Risk 100 25 + (75) 0.25 25% 200 100 10 + (90) 0.1 10% Risk ratio or Relative risk (RR) =

  18. Die (Survive) Risk 100 25 + (75) 0.25 25% 200 100 10 + (90) 0.1 10% Risk ratio or Relative risk (RR) =

  19. Die (Survive) Risk 100 25 + (75) 0.25 25% 200 0.1 10% 100 10 + (90) Risk ratio or Relative risk (RR) = 2.5

  20. Odds & Odds Ratio

  21. Odds • The ratio between the amounts staked by parties in a bet, based on the expected probability either way. • The balance of advantage or superiority.

  22. What about Die (Survive) Risk Odds? 100 25 + (75) 0.25 200 100 10 + (90) 0.1

  23. Die (Survive) Risk Odds 100 25 + (75) 0.25 200 100 10 + (90) 0.1

  24. Die (Survive) Risk Odds 100 25 + (75) 0.25 1to3 200 100 10 + (90) 0.1

  25. Die (Survive) Risk Odds 100 25 + (75) 0.25 1to3 200 100 10 + (90) 0.1

  26. Die (Survive) Risk Odds 100 25 + (75) 0.25 1to3 200 1to9 100 10 + (90) 0.1

  27. Die (Survive) Risk Odds 100 25 + (75) 0.25 1to3 200 100 10 + (90) 0.1 1to9

  28. Die (Survive) Risk Odds 100 25 + (75) 0.25 1to3 200 100 10 + (90) 0.1 1to9 Odds Ratio (O.R.) =

  29. Die (Survive) Risk Odds 100 25 + (75) 0.25 1to3 200 100 10 + (90) 0.1 1to9 Odds Ratio (O.R.) =

  30. Die (Survive) Risk Odds 100 25 + (75) 0.25 1to3 200 100 10 + (90) 0.1 1to9 Odds Ratio (O.R.) = 3

  31. Die (Survive) Risk Odds 100 25 + (75) 0.25 1to3 200 100 10 + (90) 0.1 1to9 Risk ratio or Relative risk (RR) = Odds Ratio (O.R.) = 2.5 3

  32. Measures of treatment effect influence clinicians decisions • Clinicians: • more inclined to treat if the results are presented as relative risk • less inclined to treat if the results are presented as absolute risk reduction Forrow et al. Am J Med 1992;92:121

  33. Absolute Risk Reduction • Control group event rate (CER) = Deaths / Controls • Experiment group event rate (EER) = Deaths / Treated Absolute risk reduction (difference) ARR = CER - EER

  34. Die Risk CER 100 25 0.25 25% 200 100 10 EER 0.110% Absolute Risk Reduction (ARR) =

  35. Die Risk 100 25 0.2525% 200 100 10 0.110% Absolute Risk Reduction (ARR) = 0.15 15%

  36. Number Needed to Treat NNT

  37. Clinical value of measures of treatment effect Number Needed To Treat • The odds ratio etc. not easy to understand, especially for patients. • The number needed to treat (NNT) to prevent an adverse event is a more clinically relevant measure of the consequences of treatment Sackett DL. EBM 1996; 1: 164-6 Sinclair JC. J Clin Epidemiol 1994; 47: 881-9

  38. Number Need to Treat (NNT) Out of 100 patients treated 10 died compared to 25 in the placebo group and 15 extra survived. Therefore: To get 1 more patient to survive, 6.7 (100/15) have to be treated.

  39. 100/151/ 0.15NNT = 1/ ARR

  40. Die Risk 100 25 0.2525% 200 100 10 0.110% Absolute Risk Reduction (ARR) = NNT= 1/ARR= 1/0.15= 6.7 0.15 15%

  41. Q.E.D.

  42. MAGPIE Of the patients treated (5015) 40 fitted compared to 96 in the placebo group (5055) In % Mg 0.8% vs Placebo 1.9% Therefore: ARR 1.8 – 0.8 = 1.1% (11 per 1000) To get 1 more patient to survive, 91 (100/1.1) have to be treated. = NNT

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