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Question

Difficulty: HardMeasures of Disease Frequency and Association

A regional occupational health board is evaluating the impact of night-shift work on metabolic health among healthcare workers. Demographic data indicate that 40%40\% of the nursing workforce in this region is assigned to permanent night shifts. A comprehensive longitudinal study demonstrates that the relative risk of developing type 2 diabetes mellitus over a 10-year period for night-shift nurses, compared to their day-shift counterparts, is 2.52.5. Assuming the association is causal, what percentage of the incident type 2 diabetes cases in this entire nursing population can be attributed to night-shift work? (Enter your answer as a percentage.)

Answer: 37.5 %

Answer

37.5
The Population Attributable Risk Percent (PAR%) represents the proportion of disease incidence in a total population that can be attributed to a specific exposure. When raw incidence rates are not available, PAR% can be calculated using Levin's formula: PAR%=Pe(RR−1)Pe(RR−1)+1×100PAR\% = \frac{P_e(RR - 1)}{P_e(RR - 1) + 1} \times 100, where PeP_e is the prevalence of the exposure and RRRR is the relative risk. Substituting the given values (Pe=0.40P_e = 0.40, RR=2.5RR = 2.5) yields 0.40(1.5)0.40(1.5)+1=0.601.60=0.375\frac{0.40(1.5)}{0.40(1.5) + 1} = \frac{0.60}{1.60} = 0.375, or 37.5%37.5\%.

Step-by-Step Solution

1
Identify variables from the stem
Prevalence of exposure (PeP_e) = 0.400.40; Relative risk (RRRR) = 2.52.5.
These are the two required variables to calculate the population attributable risk percent when raw incidence rates are not provided.
2
Select the appropriate epidemiological formula
PAR%=Pe(RR−1)Pe(RR−1)+1×100PAR\% = \frac{P_e(RR - 1)}{P_e(RR - 1) + 1} \times 100
Levin's formula allows calculation of the proportion of disease in the total population attributable to an exposure using only prevalence and relative risk.
3
Calculate the attributable fraction
Numerator: 0.40×1.5=0.600.40 \times 1.5 = 0.60. Denominator: 0.60+1=1.600.60 + 1 = 1.60. Fraction: 0.601.60=0.375\frac{0.60}{1.60} = 0.375.
Performing the algebraic substitution determines the decimal value of the attributable risk.
4
Convert to percentage
37.5%37.5\%
The question specifically asks for the percentage of incident cases.

Key Concept

Population Attributable Risk Percent (PAR%) using Levin's Formula
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Topics

Measures of Disease Frequency and Association

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