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Zorluk: ZorMeasures of Disease Frequency and Association

Clinical investigators are assessing the efficacy of a novel direct oral anticoagulant for the prevention of deep vein thrombosis (DVT) following total knee arthroplasty in a double-blind, placebo-controlled trial. The published results indicate that the new medication provides a Relative Risk Reduction (RRR) of 40%40\% compared to the placebo group. The authors also report that the Number Needed to Treat (NNT) to prevent one DVT event is 2020.

Based on these findings, which of the following best represents the incidence of DVT in the placebo group?

  1. A
    2.0%2.0\%
  2. B
    7.5%7.5\%
  3. C
    8.3%8.3\%
  4. 12.5%12.5\%Cevap
  5. E
    50.0%50.0\%

Cevap

The correct answer is 12.5%12.5\%.
The correct answer accurately links the formulas for Number Needed to Treat (NNT) and Relative Risk Reduction (RRR) to find the baseline incidence. First, the Absolute Risk Reduction (ARR) is calculated as 1/NNT1 / NNT, which equals 1/201/20 or 0.050.05 (5%5\%). Because RRR is defined as the ARR divided by the baseline incidence (incidence in the placebo group), rearranging the formula gives: Baseline Incidence = ARR/RRRARR / RRR. Substituting the values yields 0.05/0.40=0.1250.05 / 0.40 = 0.125, or 12.5%12.5\%.

Adım Adım Çözüm

1
Determine the Absolute Risk Reduction (ARR) from the provided Number Needed to Treat (NNT).
ARR=1NNT=120=0.05ARR = \frac{1}{NNT} = \frac{1}{20} = 0.05, which is 5%5\%.
The NNT is mathematically defined as the inverse of the ARR.
2
Recall the formula relating Relative Risk Reduction (RRR) to ARR and the baseline incidence (incidence in the placebo group, IplaceboI_{placebo}).
RRR=ARRIplaceboRRR = \frac{ARR}{I_{placebo}}
RRR represents the proportion of the baseline risk that is eliminated by the treatment intervention.
3
Rearrange the formula to solve for the incidence in the placebo group (IplaceboI_{placebo}) and substitute the known values.
Iplacebo=ARRRRR=0.050.40=0.125I_{placebo} = \frac{ARR}{RRR} = \frac{0.05}{0.40} = 0.125, which is 12.5%12.5\%.
Applying algebraic rearrangement isolates the target variable required by the question.

Anahtar Kavram

Deriving baseline incidence (Control Event Rate) using the relationships between Number Needed to Treat (NNT), Absolute Risk Reduction (ARR), and Relative Risk Reduction (RRR).
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Measures of Disease Frequency and Association

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