How is the Odds Ratio calculated?

The odds ratio is a statistical measure used primarily in epidemiology to determine the odds of an event occurring in one group relative to the odds of it occurring in another group. To calculate the odds ratio, we use the following formula:

Odds Ratio = (A/C) / (B/D)

Where:

• A is the number of cases with the event in the exposed group.

• B is the number of cases without the event in the exposed group.

• C is the number of cases with the event in the unexposed group.

• D is the number of cases without the event in the unexposed group.

This means that the odds of an event occurring in the exposed group are compared to the odds of the event occurring in the unexposed group. When expressed algebraically, the formula simplifies to (A/B) / (C/D) which reflects the preference for comparing the odds of occurrence.

In the context provided, this specific choice accurately reflects the correct calculation for the odds ratio, emphasizing how it assesses the relationship between exposure and outcome across two groups.