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Zorluk: OrtaMeasures of Association and Impact

A 45-year-old woman with severe, uncontrolled asthma asks her physician about a new monoclonal antibody she recently heard about. The physician reviews the pivotal phase III randomized, double-blind, placebo-controlled trial for the drug. The trial evaluated the incidence of severe asthma exacerbations requiring hospitalization over a 12-month period.

The study results are summarized in the following table:

GroupTotal PatientsSevere Exacerbations
Monoclonal Antibody2,5002,500150150
Placebo2,5002,500400400

Based on these trial results, which of the following is the most accurate statement regarding the drug's efficacy that the physician can share with the patient?

  1. A
    The drug reduces the absolute risk of a severe asthma exacerbation by 62.5%62.5\% compared to placebo.
  2. B
    The drug provides a 10%10\% relative risk reduction for severe asthma exacerbations compared to placebo.
  3. For every 1010 patients treated with this drug for one year, one severe asthma exacerbation is prevented.Cevap
  4. D
    For every 1616 patients treated with this drug for one year, one severe asthma exacerbation is prevented.
  5. E
    Patients taking this drug have a 2.62.6 times higher risk of experiencing a severe asthma exacerbation than those on placebo.

Cevap

For every 10 patients treated with this drug for one year, one severe asthma exacerbation is prevented.
The Number Needed to Treat (NNT) is calculated as 1ARR\frac{1}{\text{ARR}}. The Absolute Risk Reduction (ARR) is the Control Event Rate (CER) minus the Experimental Event Rate (EER). Here, CER=4002500=0.16\text{CER} = \frac{400}{2500} = 0.16 and EER=1502500=0.06\text{EER} = \frac{150}{2500} = 0.06. Thus, ARR=0.16−0.06=0.10\text{ARR} = 0.16 - 0.06 = 0.10. The NNT is 10.10=10\frac{1}{0.10} = 10, meaning 1010 patients must be treated for one year to prevent one severe exacerbation.

Adım Adım Çözüm

1
Calculate the Control Event Rate (CER).
CER = 4002500=0.16\frac{400}{2500} = 0.16 (16%16\%)
To determine the baseline risk of exacerbations in the untreated (placebo) population.
2
Calculate the Experimental Event Rate (EER).
EER = 1502500=0.06\frac{150}{2500} = 0.06 (6%6\%)
To determine the risk of exacerbations in the population receiving the monoclonal antibody.
3
Calculate the Absolute Risk Reduction (ARR).
ARR = CER−EER=0.16−0.06=0.10\text{CER} - \text{EER} = 0.16 - 0.06 = 0.10 (10%10\%)
To find the absolute difference in risk between the two groups, which is required for determining the Number Needed to Treat.
4
Calculate the Number Needed to Treat (NNT).
NNT = 1ARR=10.10=10\frac{1}{\text{ARR}} = \frac{1}{0.10} = 10
NNT represents the number of patients who must be treated to prevent one additional adverse event.

Anahtar Kavram

Absolute Risk Reduction (ARR) and Number Needed to Treat (NNT) are measures of absolute effect that provide clinical context for a treatment's benefit.
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Measures of Association and Impact

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