Risks Versus Odds

Question 1

Risk

Answer 1

Risk is a proportion
Risk describes the probability with which a health outcome (usually an adverse event) will occur.
Commonly expressed as a decimal number between 0 and 1, although it is occasionally converted into a percentage
Often expressed as a number of individuals per 1000
When the risk is 0.1, in a sample of 100 people the number of events observed will on average be 10
When the risk is 0.5, about 50 people out of every 100 will have the event

Question 2

Odds

Answer 2

Odds is a ratio
The odds is the ratio of the probability that a particular event will occur to the probability that it will not occur
Can be any number between zero and infinity
In health care it is the ratio of the number of people with the event to the number without
Commonly expressed as a ratio of two integers. For example, an odds of 0.01 is often written as 1:100, odds of 0.33 as 1:3, and odds of 3 as 3:1