What does an odds ratio compare?

What does an odds ratio compare?

• A. The odds of disease given exposure relative to the odds without exposure
• B. The hazard of disease over time
• C. The mean difference in risk between groups
• D. The absolute risk difference

Answer: (A)

The main idea tested is how the odds ratio measures the association between exposure and disease by comparing odds across exposure groups. Odds are the ratio of the probability of disease to the probability of not having disease. So the odds in those exposed is the disease probability among the exposed divided by the probability of no disease among the exposed, and similarly for those not exposed. The odds ratio is the quotient of these two odds, capturing how much more (or less) likely disease is when exposure is present compared with when it is not. This is different from hazards over time, which is about how quickly events occur (hazard ratio), and from absolute or risk differences, which look at the raw difference in probabilities between groups rather than a ratio of odds. The odds ratio is particularly useful in study designs where you can estimate odds more readily than risks, and when diseases are rare, it approximates the relative risk.

The main idea tested is how the odds ratio measures the association between exposure and disease by comparing odds across exposure groups. Odds are the ratio of the probability of disease to the probability of not having disease. So the odds in those exposed is the disease probability among the exposed divided by the probability of no disease among the exposed, and similarly for those not exposed. The odds ratio is the quotient of these two odds, capturing how much more (or less) likely disease is when exposure is present compared with when it is not.

This is different from hazards over time, which is about how quickly events occur (hazard ratio), and from absolute or risk differences, which look at the raw difference in probabilities between groups rather than a ratio of odds. The odds ratio is particularly useful in study designs where you can estimate odds more readily than risks, and when diseases are rare, it approximates the relative risk.