Attributable risk can be calculated using the following formula:
AR = Incidence in Exposed Group - Incidence in Unexposed Group
For instance, if the incidence of lung cancer in smokers is 50 per 100,000 person-years and in non-smokers is 5 per 100,000 person-years, the AR would be 50 - 5 = 45 per 100,000 person-years. This indicates that 45 out of 100,000 cases of lung cancer can be attributed to smoking.
