OnlineMedEd: Epidemiology and Stats - "Risk"

Question 1

Review the formula for probability.

Answer 1

Probability of event X = (event X) / (event X + non-event X)

Question 2

Review the formula for odds.

Answer 2

Odd of event X = (event x) / (non-event X)

Note: this is different than probability because the denominator does not account for the number of event X.

Question 3

How do you calculate relative risk?

Answer 3

RR = (probability of disease in those exposed) / (probability of disease in those not exposed)

Question 4

Why do you do that funny cross-multiple and then divide for odds ratio ([axd]/[bxc])?

Answer 4

Remember that the formula for odds ratio is a/b in the standard table. Thus, dividing the top odds ratio by the bottom odds ratio simplifies to ad/bc.

Question 5

Using the abcd nomenclature, give the formula for ARR.

Answer 5

ARR = c / (c+d) - a / (a+b)