Introduction

Attributable risk (AR) is a valuable measure in epidemiology that helps determine the proportion of disease incidence in a population that can be attributed to exposure to specific risk factors. Calculating attributable risk provides insight into the potential impact of eliminating or reducing exposure to these risk factors on overall disease incidence. In this article, we will cover how to calculate attributable risk, its importance, and some examples of its application in public health.

Understanding Attributable Risk

Before diving into how to calculate attributable risk, it is essential to understand its meaning and significance. Attributable risk can be defined as the difference between the incidence rate of a specific disease or condition among individuals exposed to a certain risk factor and those not exposed. It quantifies the proportion of cases in a population attributable to a particular risk factor and indicates the potential impact on public health if that risk factor were removed or minimized.

Calculating Attributable Risk

Calculating attributable risk involves several steps:

1. Identify the population groups: To calculate AR, you need to identify the population exposed to a specific risk factor and those who are not exposed. These groups are referred to as the exposed group (E) and the non-exposed group (NE).

2. Determine incidence rates: Calculate the incidence rates of the disease or condition for both groups separately (IR_E and IR_NE). Incidence rate is obtained by dividing the number of new cases during a given time period by the total number of individuals at risk during that same period.

3. Compute attributable risk: To obtain AR, subtract the incidence rate among non-exposed individuals (IR_NE) from the incidence rate among exposed individuals (IR_E).

AR = IR_E – IR_NE

4. Calculate attributable risk percent (AR%): To assess the proportion of cases attributable to a specific risk factor more clearly, calculate AR as a percentage.

AR% = (AR / IR_E) x 100

Example of Attributable Risk Calculation

Imagine that you are studying the impact of smoking on the incidence of lung cancer in a community. You gather the following data:

– Exposed group (smokers): 1000 people, 80 new cases of lung cancer

– Non-exposed group (non-smokers): 1000 people, 20 new cases of lung cancer

First, calculate the incidence rates for both groups:

IR_E = 80 / 1000 = 0.08

IR_NE = 20 / 1000 = 0.02

Next, compute the attributable risk:

AR = IR_E – IR_NE = 0.08 – 0.02 = 0.06

Finally, calculate the attributable risk percent:

AR% = (AR / IR_E) x 100 = (0.06 / 0.08) x 100 = 75%

In this example, the attributable risk indicates that smoking is responsible for an additional six cases per hundred people, and the attributable risk percent demonstrates that smoking accounts for 75% of all lung cancer cases among smokers in this community.

Conclusion

Attributable risk is a valuable measure in public health research and decision-making, helping to prioritize preventive measures and interventions targeting specific risk factors. By understanding how to calculate attributable risk and its significance, health professionals can better inform strategies aimed at minimizing exposure to certain risk factors and ultimately reducing disease incidence at a population level.