Definition

A measure of the likelihood of occurrence of one outcome relative to another. Odds are calculated as the probability/frequency of one outcome divided by the probability/frequency of the other. When there are only two possibilities, occurrence vs. non-occurrence, the odds are the probability of the outcome occurring divided by the probability of the outcome not occurring.

Examples

where
p = probability that the event occurs
1-p = probability that the event does not occur

Let's say the probability that a used car will work for the next 5 years is 0.6.
The probability that the used car will break down at least once during the next 5 years is (1-0.6) = 0.4.

Therefore, the odds that the used car will work for the next 5 years is 0.6/(1-0.6) = 0.6/0.4 = 1.5. The car is one and a half times more likely to work without a breakdown over the next five years, than not.

Application

If the odds > 1, the event is more likely to occur than not. If odds < 1, the event is less likely to occur than not. Odds = 1 indicates the event is equally likely to occur or not occur. Odds range from zero to infinity.

See Also

Odds Ratios, Logit