We are currently updating our website, and will have our new version online soon. Please check back later this fall.

Mailing List

Subscribe to the KT Canada mailing list




Once you have signed up, you will receive a confirmation email with your username and password. To activate your account, follow the instructions in the email.


Centre for Evidence-
Based Medicine

Completed Systematic Reviews Worksheet for Critical Care Medicine


Effectiveness of antibiotic prophylaxis in critically ill adult patients: systematic review of randomised controlled trials. BMJ 1998;316:1275-85.

Are the results of this systematic review of therapy valid?

  1. Is it a systematic review of randomised trials of the treatment you're interested in?
    Yes it included trials with random allocation and quasi-random allocation
  2. Does it include a methods section that describes finding and including all the relevant trials?
  3. Does it include a methods section that describes assessing their individual validity?
    Yes but did not use this data in the analysis and most studies had small sample size.
  4. Were the results consistent from study to study?
    Yes. There was homogeneity when studies of similar treatment route were compared.

Are the valid results of this systematic review important?

Translating odds ratios to NNTs. The numbers in the body of the table are the NNTs for the corresponding odds ratios at that particular patient's expected event rate (PEER).
Odds Ratios
0.9 0.85 0.8 0.75 0.7 0.65 0.6 0.55 0.5
Patient's Expected Event Rate (PEER) 0.05 2091 139 104 83 69 59 52 46 412
0.10 110 73 54 43 36 31 27 24 21
0.20 61 40 30 24 20 17 14 13 11
0.30 46 30 22 18 14 12 10 9 8
0.40 40 26 19 15 12 10 9 8 7
0.503 38 25 18 14 11 9 8 7 6
0.70 44 28 20 16 13 10 9 7 6
0.90 1014 64 46 34 27 22 18 15 125
  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%

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

Do these results apply to your patient?

  1. Is your patient so different from those in the overview that its results can't help you?

How great would the potential benefit of therapy actually be for your individual patient?

  1. Method I: In the table on page 1, find the intersection of the closest odds ratio from the overview and the CER that is closest to your patient's expected event rate if they received the control treatment (PEER):
    EER and CER provided in Best Evidence.
  2. Method II: To calculate the NNT for any OR and PEER:
    NNT = (1-(PEERx(1-OR))/((1-PEER)xPEERx(1-OR))
    With systemic and topical antibiotic:
    NNT for respiratory tract infection is 5, NNT for mortality is 23.
    With topical antibiotic the NNT for respiratory tract infection is 9.

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

  1. Do your patient and you have a clear assessment of their values and preferences?
    Would need to assess in individual patients
  2. Are they met by this regimen and its consequences?
    Would need to assess in individual patients

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:

  1. Do they really make biologic and clinical sense?
  2. Is the qualitative difference both clinically (beneficial for some but useless or harmful for others) and statistically significant?
  3. Was this difference hypothesised before the study began (rather than the product of dredging the data), and has it been confirmed in other, independent studies?
  4. Was this one of just a few subgroup analyses carried out in this study?

Additional Notes


Continue to CAT