Examkin

Question

Difficulty: MediumMeasures of Disease Frequency and Association

A 10-year prospective cohort study is conducted to evaluate the association between occupational exposure to silica dust and the development of pulmonary fibrosis. The study enrolls 1,500 healthy employees at a large manufacturing and mining corporation. Of these, 500 are miners exposed to high levels of silica dust, while 1,000 are administrative staff with no silica exposure. Over the 10-year follow-up period, the occurrence of newly diagnosed pulmonary fibrosis is recorded. The results are summarized in the table below:

Exposure StatusDeveloped Pulmonary FibrosisDid Not Develop Pulmonary FibrosisTotal
Silica exposure40460500
No silica exposure209801000

Assuming a causal relationship exists between silica dust exposure and pulmonary fibrosis, what percentage of the disease in the exposed group is directly attributable to the silica exposure?

  1. A
    6%
  2. B
    8%
  3. C
    25%
  4. 75%Answer
  5. E
    300%

Answer

75%
The correct answer accurately calculates the Attributable Risk Percent (ARP), also known as the etiologic fraction. ARP represents the percentage of disease in an exposed group that can be attributed solely to the exposure. It is calculated by dividing the Attributable Risk (the absolute difference in incidence between exposed and unexposed groups) by the incidence in the exposed group. In this study, the incidence in the exposed (IexposedI_{exposed}) is 40/500=0.0840/500 = 0.08 (8%8\%). The incidence in the unexposed (IunexposedI_{unexposed}) is 20/1000=0.0220/1000 = 0.02 (2%2\%). The ARP is therefore 0.08−0.020.08=0.75\frac{0.08 - 0.02}{0.08} = 0.75, or 75%75\%. Alternatively, this can be calculated from the Relative Risk (RR=0.08/0.02=4RR = 0.08 / 0.02 = 4) using the formula RR−1RR=4−14=75%\frac{RR - 1}{RR} = \frac{4 - 1}{4} = 75\%.

Step-by-Step Solution

1
Calculate the incidence of pulmonary fibrosis in the exposed group (IexposedI_{exposed}).
40/500=0.0840 / 500 = 0.08 (or 8%8\%)
Establishing the baseline risk of the outcome among those exposed to the risk factor is the first step in determining association metrics.
2
Calculate the incidence of pulmonary fibrosis in the unexposed group (IunexposedI_{unexposed}).
20/1000=0.0220 / 1000 = 0.02 (or 2%2\%)
This establishes the baseline risk of the outcome in the absence of the exposure, representing the background rate of disease.
3
Calculate the Attributable Risk Percent (ARP).
ARP=0.08−0.020.08×100=0.060.08×100=75%ARP = \frac{0.08 - 0.02}{0.08} \times 100 = \frac{0.06}{0.08} \times 100 = 75\%
The ARP formula Iexposed−IunexposedIexposed\frac{I_{exposed} - I_{unexposed}}{I_{exposed}} yields the proportion of disease in the exposed group that is directly attributable to the exposure.

Key Concept

Attributable Risk Percent (ARP)
Rate this question

Topics

Measures of Disease Frequency and Association

More questions from this topic