Question

A cohort of 3000 individuals was chosen to be part of a study on the potential relationship between being infected with hepatitis C virus (HCV) and liver disease. 800 of the cohort members acquire an HCV infection and out of those infected persons 640 develop liver disease. 200 of the remaining cohort members also develop liver disease.

A. What is the relative risk of developing liver disease based on exposure to HCV?
B. What is the odds ratio for developing liver disease based on exposure to HCV?

Answer 1

Relative risk = percentage of disease after exposition/percentage of disease without exposition

= (800/3000) / (200/3000)

= 26,66 % / 6,66 % = 400 %

Odds ratio = odds of disease after exposition/odds of disease without exposition

= (800/3000) / (200/3000)

= 0.2666 / 0.0666 = 4

Explanation:

The relative risk estimates the probable outcome in the exposed group in regard to the expected outcome in the non-exposed group. A relative risk of 400 % is indicative of 4 times the average risk. On the other hand, the odds ratio estimates the association between the exposure and the outcome for a particular disease.

Both the relative risk and the odds ratio are estimated in a very similar mode, however, the first is calculated as percentages.