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Difficulty: Very hardMeasures of Disease Frequency and Association

Match each clinical scenario or study description with its correctly calculated epidemiological measure of disease frequency or association.

  • A health department studies a population where 20%20\% of individuals are exposed to a localized environmental toxin. The incidence of chronic bronchitis is 1010 per 1,0001,000 in exposed individuals and 22 per 1,0001,000 in unexposed individuals. What percentage of chronic bronchitis cases in the overall population is specifically attributable to this toxic exposure?Population Attributable Risk Percent (PARP) ≈44.4%\approx 44.4\%
  • A case-control study evaluates the association between a novel immunosuppressant and the development of progressive multifocal leukoencephalopathy (PML). Among 200200 patients with PML, 150150 used the drug. Among 400400 healthy matched controls, 100100 used the drug. Calculate the most appropriate measure of association for this study design.Odds Ratio (OR) = 9.09.0
  • A prospective cohort study investigates the relationship between shift work and type 2 diabetes. Over a 1010-year period, the incidence of diabetes is 15%15\% in shift workers and 5%5\% in day workers. What proportion of diabetes cases among the shift workers can be directly attributed to their work schedule?Attributable Risk Percent (ARP) ≈66.7%\approx 66.7\%
  • An occupational health study tracks a cohort of miners over a 1010-year period. Based on age- and sex-matched national demographic data, 2020 deaths from lung cancer were expected in this population. However, 5050 deaths from lung cancer were observed during the study period. Calculate the appropriate measure to express this mortality comparison.Standardized Mortality Ratio (SMR) = 250%250\%
  • During a local outbreak of a novel respiratory pathogen, public health officials identify 1010 primary cases. These individuals live with a total of 150150 susceptible household contacts. Over the next two weeks, 3030 of these household contacts develop the infection. Calculate the measure that best reflects the disease's infectivity in close-contact settings.Secondary Attack Rate = 20%20\%

Answer

The correct pairings match the environmental toxin scenario with PARP (≈44.4%\approx 44.4\%), the PML case-control study with OR (9.09.0), the shift worker cohort with ARP (≈66.7%\approx 66.7\%), the miners mortality data with SMR (250%250\%), and the respiratory outbreak with Secondary Attack Rate (20%20\%). Each calculation derives strictly from matching the specific study design with its unique epidemiological formula.
Each scenario describes a unique study design or clinical question that mandates a specific epidemiological measure. By calculating the correct metric (PARP, OR, ARP, SMR, Secondary Attack Rate) using the provided numerical data, each scenario correctly matches a single mathematical output.

Step-by-Step Solution

1
Calculate the Population Attributable Risk Percent (PARP) for the environmental toxin scenario.
PARP ≈44.4%\approx 44.4\%
The question asks for the percentage of disease in the overall population attributable to the exposure. First, calculate the total population incidence (IpI_p): Ip=(10×0.20)+(2×0.80)=2+1.6=3.6I_p = (10 \times 0.20) + (2 \times 0.80) = 2 + 1.6 = 3.6 per 1,0001,000. Then apply the formula: PARP=Ip−IunexposedIp=3.6−23.6=1.6/3.6≈44.4%PARP = \frac{I_p - I_{unexposed}}{I_p} = \frac{3.6 - 2}{3.6} = 1.6 / 3.6 \approx 44.4\%.
2
Calculate the appropriate association measure for the progressive multifocal leukoencephalopathy (PML) case-control study.
Odds Ratio (OR) = 9.09.0
Case-control studies require Odds Ratios. Construct a 2x2 table: Cases exposed (aa) = 150150, Cases unexposed (cc) = 5050. Controls exposed (bb) = 100100, Controls unexposed (dd) = 300300. OR=a×db×c=150×300100×50=450005000=9.0OR = \frac{a \times d}{b \times c} = \frac{150 \times 300}{100 \times 50} = \frac{45000}{5000} = 9.0.
3
Calculate the proportion of diabetes cases among shift workers attributable to shift work.
Attributable Risk Percent (ARP) ≈66.7%\approx 66.7\%
The question asks for ARP, which represents the excess risk among the exposed. ARP=Incidenceexposed−IncidenceunexposedIncidenceexposed=0.15−0.050.15=0.100.15=23≈66.7%ARP = \frac{\text{Incidence}_{exposed} - \text{Incidence}_{unexposed}}{\text{Incidence}_{exposed}} = \frac{0.15 - 0.05}{0.15} = \frac{0.10}{0.15} = \frac{2}{3} \approx 66.7\%.
4
Calculate the appropriate measure for the occupational mortality data.
Standardized Mortality Ratio (SMR) = 250%250\%
When comparing observed deaths in a specific cohort to expected deaths based on a standardized population, use SMR. SMR=ObservedExpected×100=5020×100=250%SMR = \frac{\text{Observed}}{\text{Expected}} \times 100 = \frac{50}{20} \times 100 = 250\%.
5
Calculate the infectivity measure for the respiratory outbreak.
Secondary Attack Rate = 20%20\%
Secondary Attack Rate measures the spread to susceptible close contacts. Secondary cases = 3030, total susceptible contacts = 150150. Rate = 30150×100=20%\frac{30}{150} \times 100 = 20\%.

Key Concept

Selecting the correct epidemiological measure of frequency or association relies on identifying the study design (e.g., Odds Ratio for case-control) or the specific outcome of interest (e.g., PARP for population impact, SMR for mortality comparison).
Estimated Time:3m 0s
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Measures of Disease Frequency and Association

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