A set of training materials for professionals working in intervention epidemiology, public health microbiology and infection control and hospital hygiene.
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The second type of question we may ask relates to the excess risk of disease in the total population that is attributable to exposure. This is the attributable risk in the population (ARpop) or the population attributable risk. It is the proportion of cases in the general population that can be attributed to the exposure.
Ipop = incidence in population
Iu = incidence among unexposed
It represents the reduction in risk we would achieve if the entire population was not exposed. It helps to identify which exposures are most relevant in the community and will yield most benefit from public health interventions  .
The population attributable risk can also be expressed as a percentage of the total risk in the population.
This is known as the attributable fraction in the population (AFpop):
Ipop = incidence in the population
Iu = incidence among the exposed
No. of deaths
Risk of death per 1,000
Attributable risk (population)
18 - 10 = 8/1,000
This means that (if speeding causes driving related deaths) 44% of driving related deaths in the population can be attributed to speeding.
18 - 14 = 4/1,000
This means that (if drunk driving causes driving related deaths) 22% of driving related deaths in the population can be attributed to drunk driving.
AFpop can also be expressed as:
The above formula is not valid if the RR is adjusted for confounders, as is often the case. In this situation one of the following alternatives is preferable:
Pe = proportion of the population exposed
PCe = proportion of cases exposed
Ie = incidence in exposed
Iu = incidence in unexposed
RR = risk ratio
ARe = attributable risk among exposed
If the risk factor is causal, then the population attributable risk depends on:
To have a large impact on the population, the exposure must be common.
Methods are also available for dealing with multiple exposure categories for a single risk factor , and for diseases caused by multiple risk factors  .
Sometimes, diseases are the result of complex interactions between risk factors. Methods to conceptualise and clarify these interactions have been developed. These include sequential attributable fractions  , and causal pies  .
The number of cases (amount of disease) within the population that can be attributed to the exposure
The proportion of cases (percentage of disease) within the population that can be attributed to the exposure
What is the proportion of disease within the population that:
Attributable fraction (population)
Population attributable fraction
Attributable proportion (population)
Aetiological fraction / Preventable fraction (population)
Population attributable risk percent
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