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Zorluk: ZorMeasures of Association and Impact

A neurologist is evaluating whether to incorporate a newly approved disease-modifying therapy into their clinical practice for patients with moderate-to-severe relapsing-remitting multiple sclerosis (RRMS). To make an evidence-based decision, the physician reviews a recent phase III trial published in a prominent medical journal. The study included 3,2003,200 adult patients with RRMS who were randomly assigned in a 1:11:1 ratio to receive either the new therapy or a placebo over a 2424-month period.

During the study period, 6464 of the 1,6001,600 patients receiving the new therapy experienced a confirmed clinical relapse. In contrast, 112112 of the 1,6001,600 patients in the placebo group experienced a confirmed clinical relapse. The authors of the study report a relative risk of 0.570.57 for clinical relapse (95%95\% CI, 0.430.43 to 0.760.76; p=0.003p = 0.003).

Based on the data provided, which of the following is the most accurate interpretation regarding the efficacy and clinical impact of this new therapy?

  1. A
    The therapy provides a statistically significant reduction in clinical relapses, and approximately 33 patients must be treated to prevent one clinical relapse.
  2. B
    The therapy provides a statistically significant reduction in clinical relapses, and approximately 43 patients must be treated to prevent one clinical relapse.
  3. C
    The therapy does not provide a statistically significant reduction in clinical relapses because the 95% confidence interval for the relative risk does not include zero.
  4. The therapy provides a statistically significant reduction in clinical relapses, and approximately 34 patients must be treated to prevent one clinical relapse.Cevap
  5. E
    The observed reduction in clinical relapses is likely due to effect modification rather than a true treatment effect, as the relative risk is less than 1.0.

Cevap

The therapy provides a statistically significant reduction in clinical relapses, and approximately 34 patients must be treated to prevent one clinical relapse.
The study results demonstrate a statistically significant reduction in clinical relapses because the 95% confidence interval for the relative risk (0.430.43 to 0.760.76) does not include the null value for ratio measures, which is 1.01.0. To determine the practical clinical impact, the physician must calculate the Absolute Risk Reduction (ARR), which is the difference between the control event rate (112/1600=0.07112/1600 = 0.07) and the experimental event rate (64/1600=0.0464/1600 = 0.04). This yields an ARR of 0.030.03. The Number Needed to Treat (NNT) is the inverse of the ARR (1/0.03=33.331/0.03 = 33.33). By rigorous biostatistical convention, NNT is always rounded up to the next whole integer (the ceiling function) to provide a conservative estimate of benefit. Treating 3333 patients is insufficient to prevent one full event (33×0.03=0.9933 \times 0.03 = 0.99), thus 3434 patients must be treated.

Adım Adım Çözüm

1
Determine the statistical significance of the findings.
The relative risk (RR) is 0.57, and its 95% confidence interval (0.43 to 0.76) does not cross the null value for ratios, which is 1.0.
To establish if the therapy is genuinely effective and statistically sound before calculating its clinical impact.
2
Calculate the Absolute Risk Reduction (ARR).
Control Event Rate (CER) = 112 / 1600 = 0.07. Experimental Event Rate (EER) = 64 / 1600 = 0.04. ARR = 0.07 - 0.04 = 0.03 (or 3%).
ARR is required as the denominator to determine the Number Needed to Treat (NNT).
3
Calculate the Number Needed to Treat (NNT) and apply the correct rounding rule.
NNT = 1 / ARR = 1 / 0.03 = 33.33. According to biostatistical convention, NNT must always be rounded UP to the nearest whole number (ceiling function), resulting in 34.
Rounding up ensures that the clinical benefit is not overstated. Treating 33 patients would theoretically prevent only 0.99 of an event, so 34 must be treated to guarantee the prevention of at least one whole event.

Anahtar Kavram

Absolute Risk Reduction (ARR) calculation and the conservative rounding rule (ceiling) for Number Needed to Treat (NNT).
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