ABIM & Internal Medicine Shelf Exam Review Question of the Week: Calculating the Relative Risk Ratio (RRR)
Internal Medicine Board Exam Practice QuestionAs we begin #GenMed Week in our preparation of the ABIM and Internal Medicine Shelf exam, here is a question directly out of the Knowmedge QVault. Give it your best shot and then see below for the answer.
In a study, 2,800 patients were examined.
● 1,000 patients who have a long standing history of alcoholism develop cirrhosis
● 750 patients who have long standing history of alcoholism do not develop cirrhosis
● 50 patients who don’t drink alcohol develop cirrhosis
● 1,000 patients who don’t drink alcohol don’t develop cirrhosis
What is the relative risk ratio (RRR) of patients who drink alcohol and develop liver cirrhosis versus patients who don’t drink alcohol but still develop liver cirrhosis?
A. 5 B. 12 C. 20 D. 40 E. 100
ABIM Exam Practice Question Explanation
Relative risk ratio (RRR) is the ratio of incidence of developing a disease when exposed to a risk factor divided by the incidence of developing a disease when not exposed to that risk factor. We know that alcohol can cause cirrhosis. To calculate the relative risk ratio, we first take the number of people who develop cirrhosis when exposed to alcohol (1000) and divide it by the total number of patients who drink alcohol (1000+750) or 1000/1750. We then calculate the incidence of cirrhosis in patients who were not exposed to alcohol (50) and divide it by the total number of patients who don’t drink alcohol (1000+50) or 50/1050. We now take 1000/1750 and divide it by 50/1050 to get Choice B (12). This means that the incidence of cirrhosis of liver is increased by 12 times in patients exposed to alcohol.
The best way to understand this is by letter variables
A = incidence of disease with exposure
B = no disease with exposure
C = incidence of disease without exposure
D = no disease without exposure
The general formula for relative risk ratio is A/(A+B) divided by C/(C+D).
You can view all the previous ABIM Exam Review Questions of the Week at the Knowmedge Blog. You can also find additional topics and questions directly from the Knowmedge Internal Medicine ABIM Board Exam Review Questions QVault.