# How do you calculate PAF?

**Calculating PAF**

- Pi = proportion of population at exposure level i, current exposure.
- P'i = proportion of population at exposure level i, counterfactual or ideal level of exposure.
- RR = the relative risk at exposure level i.
- n = the number of exposure levels.

Similarly one may ask, how do you calculate population etiologic fraction?

**Etiologic fraction** = [ a / ( a + b ) − c / ( c + d ) ] 1 − [ c / ( c + d ) ] (**population attributable** risk). The relative risk used by epidemiologists for prospective studies differs slightly from the odds ratio used in case–control studies and is defined as a/(ac)/b(bd).

**incidence**proportion can be

**calculated**as 16 ⁄ 2,100 = 7.6 cases per 1,000 population during the four-year period, or an average of 1.9 cases per 1,000 per year (7.6 divided by 4 years).

Hereof, what is the formula for the population attributable risk?

Calculating the **population attributable risk** percent allows you to determine what percent of an outcome could possibly be prevented if a **risk** factor were to be removed from the **population**. To calculate the **attributable risk**, one simply subtracts the **risk** for the non-exposed group from the **risk** for the exposed group.

The **formula** on the right shows that the **attributable risk** is related to the **relative risk**, but instead of it being the ratio of the incidence rates, it is the difference between them. **Attributable risk** is the difference in the probability of disease in exposed people and the probability of disease in unexposed people.