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Centre for Evidence-
Based Medicine

Systematic Review (of Therapy) Critical Appraisal Worksheet

Download this worksheet [Word document; 33.5kb]

Are the results of this systematic review valid?





Are the valid results of this systematic review important?

Translating odds ratios to NNTs:
The numbers in the body of the tables are the NNTs for the corresponding odds ratio at that particular patient's expected event rate (PEER).

When the odds ratio (OR) < 1
This table applies when a bad outcome is prevented by therapy.
Odds Ratios
0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 0.5 0.4 0.3 0.2
Patient's Expected Event Rate (PEER) 0.05 2091 139 104 83 69 59 52 46 412 34 29 26
0.10 110 73 54 43 36 31 27 24 21 18 15 13
0.20 61 40 30 24 20 17 14 13 11 10 8 7
0.30 46 30 22 18 14 12 10 9 8 7 5 5
0.40 40 26 19 15 12 10 9 8 7 6 4 4
0.503 38 25 18 14 11 9 8 7 6 5 4 3
0.70 44 28 20 16 13 10 9 7 6 5 4 3
0.90 1014 64 46 34 27 22 18 15 125 9 4 3
  1. The relative risk reduction (RRR) here is 10%
  2. The RRR here is 49%
  3. For any OR, NNT is lowest when PEER = .50
  4. The RRR here is 1%
  5. The RRR here is 9%
  1. For any OR, NNT is lowest when PEER = .50
When the odds ratio (OR) > 1
This table applies both when a good outcome is increased by therapy and when a side-effect is caused by therapy
Odds Ratios
1.1 1.25 1.5 1.75 2 2.25 2.5 2.75 3 3.5 4 5
Patient's Expected Event Rate (PEER) 0.05 212 86 44 30 23 18 16 14 12 10 9 7
.10 113 46 24 16 13 10 9 8 7 6 5 4
.20 64 27 14 10 8 7 6 5 5 4 4 3
.30 50 21 11 8 7 6 5 5 4 4 3 3
.40 44 19 10 8 6 5 5 5 4 4 3 3
.501 42 18 10 8 6 6 5 5 4 4 4 3
.70 51 23 13 10 9 8 7 7 6 6 5 5
.90 121 55 33 25 22 19 18 17 16 15 14 13

Can you apply this valid, important evidence from a systematic review in caring for your patient?

Do these results apply to our patient?



What are your patient's potential benefits and harms from the therapy



Are your patient's values and preferences satisfied by the regimen and its consequences?



Should you believe apparent qualitative differences in the efficacy of therapy in some subgroups of patients?

Only if you can say "yes" to all of the following: