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Centre for Evidence-
Based Medicine

Completed Therapy Worksheet II for Evidence-Based Gastroenterology and Hepatology

Citation

Lack of effect of treating helicobacter pylori infection in patients with nonulcer dyspepsia. Blum A.L. et al N Engl J Med 1998;339:1875-81.

Are the results of this single preventive or therapeutic trial valid?

  1. Was the assignment of patients to treatments randomised?
    And was the randomisation list concealed?
    Yes
  2. Were all patients who entered the trial accounted for at its conclusion?
    And were they analysed in the groups to which they were randomised?
    Yes
  3. Were patients and clinicians kept "blind" to which treatment was being received?
    Yes. The study was placebo controlled.
  4. Aside from the experimental treatment, were the groups treated equally?
    Yes
  5. Were the groups similar at the start of the trial?
    No. 66% of the eradication group were men compared to 76% of omeprazole alone group.

Are the valid results of this randomised trial important?

Sample Calculations

Occurrence of symptoms Relative Risk Reduction
RRR
Absolute Risk Reduction
ARR
Number Needed to Treat
NNT
Omeprazole alone Symptoms
"control" Event Rate
CER
Hp eradication Symptoms
Experimental Event Rate
EER
(CER - EER)/CER CER - EER 1/ARR
79.3% 72.6% (79.3% - 72.6%)/79.3%
= 8.4%
79.3% - 72.6%
= 6.7%
1/6.7%
= 15pts

95% Confidence Interval (CI) on an NNT
= 1 / (limits on the CI of its ARR)
= +-1.96 sqrt(((CERx(1-CER))/(# of control pts.)) + ((EERx(1-EER))/(# of exper. pts.)))
= 9.2%

Your Calculations

Relative Risk Reduction
RRR
Absolute Risk Reduction
ARR
Number Needed to Treat
NNT
CER EER (CER - EER)/CER CER - EER 1/ARR
0.793 0.726 (0.793 - 0.726)/0.793
= 8.4%
0.067 15

Can you apply this valid, important evidence about a treatment in caring for your patient?

Do these results apply to your patient?

  1. Is your patient so different from those in the trial that its results can't help you?
    Yes, she is similar to those patients included in the trial

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

  1. Method I: f
    Risk of the outcome in your patient, relative to patients in the trial. expressed as a decimal: 1.0

    NNT/F
    = 15/1
    = 15 (NNT for patients like yours)
  2. Method II: 1 / (PEER x RRR)
    Your patient's expected event rate if they received the control treatment: PEER:______

    1 / (PEER x RRR)
    = 1/________
    = _______(NNT for patients like yours)

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?
    Needs to be assessed in each patient
  2. Are they met by this regimen and its consequences?
    Needs to be assessed in each patient

Additional Notes

The eradication group contained a higher proportion of women than the control group. If there is a sex difference in response to treatment the study might have over or underestimated the effect. I might question the validity of this study. Analysis of the data on a "per-protocol" basis provides a higher NNTof 23 due to the large number of exclusions in both randomisation limbs.

Comments on the 2 Studies

  • The McColl study had greater validity in that the two groups of randomised patients were better matched and there were no exclusions after randomisation.
  • The power of the McColl study was greater due to the larger number of patients treated and analysed.
  • The McColl study is more widely applicable in that the definition of dyspepsia was broad and a broad range of severity of symptoms was included.

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