Final answer:
The ratio of two rates, known as relative risk, compares the incidence of an outcome in an exposed group to that in a non-exposed group and is often expressed as a percentage to clarify the likelihood of occurrence.
Step-by-step explanation:
To define a ratio of two rates (percentages) that indicate the extent to which one entity is more likely than another to experience an outcome, we often refer to the measure known as relative risk. The relative risk is a crucial indicator in cohort studies, particularly in the field of epidemiology. It compares the incidence of a health-related event in a group exposed to a certain factor versus a group that is not exposed. To calculate the relative risk, use the following formula:
Relative Risk (RR) = (Incidence rate in the exposed group) / (Incidence rate in the non-exposed group)
Relative risk is often converted into a percentage for better comprehension. The incidence rate in a population might be expressed per 100, 1,000, or even 100,000 individuals to make it more relatable. For example, an incidence rate of breast cancer in a study might be 0.025, which converts to 2.5% or 25 cases per 1,000 women per year. Similarly, when calculating relative frequencies, the relative frequency is used to describe how often a certain outcome occurs relative to the total number of outcomes, enriching our ability to compare rates or probabilities.