Attributable risk

Attributable Risk

Attributable risk, also known as the risk difference, is a measure used in epidemiology to determine the proportion of incidence of a disease in the exposed group that can be attributed to the exposure. It is a crucial concept in public health and clinical research, as it helps to quantify the impact of a risk factor on the occurrence of a disease.

Definition

Attributable risk is defined as the difference in the rate of a condition between an exposed population and an unexposed population. Mathematically, it is expressed as:

AR = I_e - I_u

where:

• AR is the attributable risk.
• I_e is the incidence rate of the disease in the exposed group.
• I_u is the incidence rate of the disease in the unexposed group.

Interpretation

Attributable risk provides insight into the public health impact of removing a risk factor. For example, if smoking is a risk factor for lung cancer, the attributable risk would indicate how many cases of lung cancer could be prevented if smoking were eliminated.

Applications

Attributable risk is used in various fields, including:

• Public health: To design and evaluate interventions aimed at reducing exposure to risk factors.
• Clinical research: To assess the potential benefits of removing or reducing exposure to a risk factor.
• Health policy: To inform policy decisions and prioritize resource allocation.

Calculation Example

Suppose a study finds that the incidence of lung cancer among smokers (I_e) is 200 per 100,000 person-years, while the incidence among non-smokers (I_u) is 20 per 100,000 person-years. The attributable risk would be:

AR = 200 - 20 = 180 per 100,000 person-years.

This means that 180 cases of lung cancer per 100,000 person-years can be attributed to smoking.

Limitations

While attributable risk is a valuable measure, it has limitations:

• It assumes a causal relationship between exposure and disease, which may not always be valid.
• It does not account for confounding factors that may influence the association.
• It is not applicable to case-control studies, where odds ratios are used instead.

Also see

• Relative risk
• Risk factor
• Epidemiology
• Public health
• Preventive medicine