Final answer:
The calculated value when a population is exposed to a specific agent is relative risk.
Step-by-step explanation:
When the population is exposed to a specific agent, the calculated value is the relative risk. Relative risk is calculated by dividing the incidence of the health event for the exposed group by the incidence of the health event in the unexposed group. It provides a measure of how much more likely the exposed group is to experience the health event compared to the unexposed group. For example, if the relative risk is 3.25, it means the exposed group is 3.25 times more likely to have the health event than the unexposed group.