A team of epidemiologists conducts a case-control study to evaluate the association between the use of a novel agricultural herbicide and the development of a rare form of non-Hodgkin lymphoma. They recruit 100 patients recently diagnosed with this specific lymphoma (cases) and 400 healthy age- and sex-matched individuals from the same region (controls).
The exposure histories of both groups are summarized in the table below:
| Exposure Status | Cases (Lymphoma) | Controls (Healthy) |
|---|---|---|
| Exposed to herbicide | 80 | 200 |
| Not exposed to herbicide | 20 | 200 |
| Total | 100 | 400 |
The annual incidence of this specific non-Hodgkin lymphoma in the general population is approximately 3 per 100,000.
Based on these findings, what percentage of the lymphoma cases among the exposed workers can be attributed to this herbicide exposure?
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- Answer
- E
Answer
The percentage of the lymphoma cases among the exposed workers that can be attributed to the herbicide exposure is .
The question asks for the Attributable Risk Percent (ARP) in the exposed group. Because this is a case-control study, relative risk (RR) cannot be calculated directly. However, the disease is stated to be rare (incidence 3 per 100,000), which satisfies the rare disease assumption. This allows the Odds Ratio (OR) to be used as a reliable estimate of RR. First, calculate the OR: (Odds of exposure in cases) / (Odds of exposure in controls) = (80/20) / (200/200) = 4 / 1 = 4. Next, substitute the OR into the ARP formula: ARP = (RR - 1) / RR ≈ (OR - 1) / OR = (4 - 1) / 4 = 3/4 = 75%.
Step-by-Step Solution
Key Concept
In a case-control study analyzing a rare disease, the Odds Ratio (OR) accurately approximates the Relative Risk (RR) and can be substituted into the Attributable Risk Percent formula: ARP = (OR - 1) / OR.