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Zorluk: Çok zorMeasures of Association and Impact

Investigators recently published findings from a prospective, multicenter trial assessing a new targeted biologic therapy for moderate-to-severe Crohn's disease. Over a 5-year observation period, the primary outcome measured was the requirement for surgical bowel resection. Data showed that 28% of individuals in the control arm (receiving standard care plus placebo) required surgical intervention. In contrast, researchers noted that the addition of the new biologic yielded a 25% relative risk reduction (RRR) for this primary outcome. The authors specified the 95% confidence interval (CI) for the RRR as 12% to 38%. Utilizing these reported parameters, which of the following correctly identifies the number needed to treat (NNT) to prevent one surgical resection over the 5-year period, along with the correct 95% CI for the relative risk (RR)?

  1. NNT = 15; 95% CI for RR = 0.62 to 0.88Cevap
  2. B
    NNT = 14; 95% CI for RR = 0.62 to 0.88
  3. C
    NNT = 4; 95% CI for RR = 0.62 to 0.88
  4. D
    NNT = 34; 95% CI for RR = 0.62 to 0.88
  5. E
    NNT = 15; 95% CI for RR = 0.12 to 0.38

Cevap

NNT = 15; 95% CI for RR = 0.62 to 0.88
The correct answer accurately synthesizes three distinct steps. First, it derives the ARR by multiplying the control incidence by the RRR (0.28×0.25=0.070.28 \times 0.25 = 0.07). Second, it correctly calculates the NNT as 1/0.07=14.281 / 0.07 = 14.28 and applies the mandatory clinical rounding rule (always round UP for NNT), resulting in 15. Finally, it correctly translates the RRR confidence interval to an RR confidence interval by subtracting the RRR bounds from 1, mapping 12% to 0.88 and 38% to 0.62.

Adım Adım Çözüm

1
Calculate the Absolute Risk Reduction (ARR)
ARR=0.28×0.25=0.07ARR = 0.28 \times 0.25 = 0.07
ARR is derived by multiplying the baseline risk (control event rate) by the Relative Risk Reduction (RRR).
2
Calculate the raw Number Needed to Treat (NNT)
NNT=10.07=14.28NNT = \frac{1}{0.07} = 14.28
NNT is the inverse of the Absolute Risk Reduction.
3
Apply the strict statistical rounding rule for NNT
Round 14.28 up to 15
NNT must ALWAYS be rounded UP to the next whole number (ceiling function) because treating 14 people would only prevent 0.98 events. You must treat a full 15 people to guarantee the prevention of at least one event.
4
Determine the 95% CI for the Relative Risk (RR)
Lower bound: 1−0.38=0.621 - 0.38 = 0.62; Upper bound: 1−0.12=0.881 - 0.12 = 0.88
The relationship is RR=1−RRRRR = 1 - RRR. The upper limit of the RRR corresponds to the lower limit of the RR, and vice versa.

Anahtar Kavram

Converting Relative Risk Reduction to Absolute Risk Reduction, applying clinical ceiling rounding rules for NNT, and understanding the mathematical relationship between RR and RRR intervals.
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Konular

Measures of Association and Impact

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