Measures of Risk

Attributable Risk Exercise

Epidemiologic research not only focuses on the identification and assessment of risk factors but
also the planning and evaluating of public health interventions or control measures to reduce
the incidence of disease in the population. Being able to predict the impact of removing a
particular exposure on the risk of developing a disease is an important public health
consideration because it allows public health planners to make decisions about allocating
scarce resources (time, energy, money and political capital) for the greatest impact.

Measures of Attributable Risk answer the following questions:
1. What amount of the risk of developing a disease is attributable to a particular
exposure?
2. By what percent would the risk of developing disease be reduced if the exposure
were eliminated?
For public health decision-making purposes, it is valuable to be able to answer these questions
from two perspectives: the impact of eliminating the exposure on only those who are exposed
and impact of eliminating the exposure on the entire population.

Question 1: The preventive advantages of eating fish have been reported in numerous studies.
A cohort study reported that never or rarely eating fish increased the risk for stroke.
a) Calculate the incidence of stroke in persons who eat fish 0-1 times per week.

b) Calculate the incidence of stroke in persons who eat fish 2+ times per week.

c) Calculate and interpret the Relative Risk for the association between eating fish and
stroke.

d) Calculate and interpret the attributable risk among persons who never or rarely eat fish.

e) Calculate and interpret the attributable risk percent among persons who never or rarely
eat fish.

If persons who never or rarely eat fish change their eating habits and begin to eat fish 2 or more
times per week, their incidence of strokes would decrease by 21.6 per 1,000 individuals (AR =
21.6 per 1,000), which would represent a 43% reduction of the incidence of strokes in persons
who never or rarely eat fish (AR% = 43%).
f) Calculate and interpret the population attributable risk.

g) Calculate and interpret the population attributable risk percent.

Question 2: In a cohort study of smoking and lung cancer, the incidence of lung cancer among
current smokers was 9/1,000 and 45% of the total population were current smokers. The
incidence among current nonsmokers was 1/1,000.
a) The incidence of lung cancer attributable to smoking in the total population is:

b) The proportion attributable risk in the total population that is attributable to smoking is: