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Difficulty: HardMeasures of Disease Frequency and Association

Occupational health physicians are investigating the respiratory effects of prolonged exposure to a novel industrial solvent used in paint manufacturing. A longitudinal study follows employees at several facilities over a 10-year period. The study includes 1,5001,500 floor workers who directly handle the solvent and 4,5004,500 administrative staff at the same facilities who have no direct solvent exposure. Over the study duration, 120120 of the floor workers and 9090 of the administrative staff are newly diagnosed with adult-onset asthma. Based on these results, what percentage of the asthma cases among the floor workers is theoretically attributable to their solvent exposure?

Answer: 75 %

Answer

75
The question asks for the percentage of asthma cases among the solvent-handling workers (the exposed group) that is attributable to their exposure. This specifically describes the Attributable Risk Percent (ARP) or Etiologic Fraction. First, calculate the incidence in the exposed group (IeI_e): 120120 cases / 1,5001,500 workers = 0.080.08 (or 8%8\%). Next, calculate the incidence in the unexposed group (IuI_u): 9090 cases / 4,5004,500 workers = 0.020.02 (or 2%2\%). The formula for ARP is Ie−IuIe×100\frac{I_e - I_u}{I_e} \times 100. Plugging in the values gives 0.08−0.020.08×100=0.060.08×100=75%\frac{0.08 - 0.02}{0.08} \times 100 = \frac{0.06}{0.08} \times 100 = 75\%. Therefore, 75%75\% of the asthma cases in the floor workers are theoretically caused by the solvent exposure.

Step-by-Step Solution

1
Calculate the incidence of asthma in the exposed group (floor workers).
Ie=1201500=0.08I_e = \frac{120}{1500} = 0.08 (or 8%8\%).
Incidence in the exposed (IeI_e) is required to determine baseline risk associated with the exposure.
2
Calculate the incidence of asthma in the unexposed group (administrative staff).
Iu=904500=0.02I_u = \frac{90}{4500} = 0.02 (or 2%2\%).
Incidence in the unexposed (IuI_u) represents the baseline risk of the disease in the absence of the specific exposure.
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 question asks for the percentage of disease 'among the floor workers' (exposed group) that is attributable to the exposure, which is the definition of ARP.

Key Concept

Attributable Risk Percent (ARP) measures the proportion of disease cases in an exposed population that is directly attributable to the exposure. It is calculated as Ie−IuIe×100\frac{I_e - I_u}{I_e} \times 100 or RR−1RR×100\frac{RR - 1}{RR} \times 100.
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Topics

Measures of Disease Frequency and Association

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