Match each clinical research scenario below with its correctly calculated epidemiological … — USMLE Step 3

Match each clinical research scenario below with its correctly calculated epidemiological measure of association or impact.

A randomized controlled trial reports that $10\%$ of patients on placebo and $6\%$ of patients on a novel drug experience a recurrent myocardial infarction over $2$ years. Calculate the Number Needed to Treat (NNT). $25$
A prospective cohort study follows $2,000$ smokers and $8,000$ non-smokers. Chronic bronchitis develops in $200$ smokers and $400$ non-smokers. Calculate the Relative Risk (RR). $2.0$
A case-control study includes $100$ patients with a rare liver tumor and $100$ healthy controls. Sixty cases and twenty controls have a history of vinyl chloride exposure. Calculate the Odds Ratio (OR). $6.0$
A clinical trial evaluates a new immunosuppressant. Severe opportunistic infections occur in $9\%$ of the treatment group and $4\%$ of the placebo group. Calculate the Number Needed to Harm (NNH). $20$
An occupational cohort study finds the incidence of peripheral neuropathy is $20\%$ in workers exposed to a specific solvent and $5\%$ in unexposed workers. Calculate the Attributable Risk Percent (ARP) in the exposed group. $75\%$

The scenarios match the following calculations: NNT = 25, RR = 2.0, OR = 6.0, NNH = 20, and ARP = 75%.

Each scenario provides specific data that directly plug into standard biostatistical equations. The NNT is

\frac{1}{ARR}

(

25

). The RR is the ratio of incidences (

2.0

). The OR is the ratio of odds of exposure (

6.0

). The NNH is

\frac{1}{ARI}

(

20

). The ARP is the proportion of risk in the exposed attributable to the exposure (

75\%

Calculate the Number Needed to Treat (NNT).

NNT = 25

NNT is the inverse of the Absolute Risk Reduction (ARR).

ARR = 0.10 - 0.06 = 0.04

, so

NNT = \frac{1}{0.04} = 25

Calculate the Relative Risk (RR).

RR = 2.0

RR is the incidence in the exposed divided by incidence in the unexposed.

RR = \frac{200/2000}{400/8000} = \frac{0.10}{0.05} = 2.0

Calculate the Odds Ratio (OR).

OR = 6.0

OR for a case-control study is

\frac{a \times d}{b \times c}

where

a=60

c=40

b=20

d=80

OR = \frac{60 \times 80}{20 \times 40} = 6.0

Calculate the Number Needed to Harm (NNH).

NNH = 20

NNH is the inverse of Absolute Risk Increase (ARI).

ARI = 0.09 - 0.04 = 0.05

, so

NNH = \frac{1}{0.05} = 20

Calculate the Attributable Risk Percent (ARP).

ARP = 75\%

ARP is calculated as

\frac{\text{Incidence}_{exposed} - \text{Incidence}_{unexposed}}{\text{Incidence}_{exposed}} = \frac{0.20 - 0.05}{0.20} = 75\%

Measures of Association and Impact calculations

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