In general, all individuals, whether they have or have not been exposed to a risk factor, have some chance of developing a disease if no prevention measures have been taken. The AR/AF estimates the risk above and beyond this baseline risk that all people have. It is graphically represented on slide 11. Formulas for calculating AR and AF are described on slides 11 and 12, respectively.

Example:
Using the data presented in slide 8, the attributable risk associated with smoking is 0.96/1000/yr – 0.7/1000/yr = 0.89/1000/yr. The incidence of lung cancer attributed to smoking is 0.89/1000/yr.

The proportion of lung cancer cases that could be prevented in this population of smokers if they would quit smoking is 0.89/1000/yr divided by 0.96/1000/yr = 92.7%.