Definition
Even chance
An event has an even chance when its probability is exactly one half.
What it means
This is a true 50–50 situation. There is the same amount of chance for the event to happen as for it not to happen. It does not promise that short runs will split perfectly in half.
Remember it
Picture a level balance: “happens” and “does not happen” carry equal chance.
Example
A bag holds four green counters and four orange counters. Without looking, one counter is drawn. The chance of green is 4 out of 8, or 1/2, so drawing green has an even chance.
Watch for
A bag with five green counters and three orange counters does not give green an even chance; green has probability 5/8.
Common mix-up
Even chance does not mean results must alternate or that exactly half of a small number of trials will succeed.
Exact meaning
In a stated probability model, an event has an even chance when the event and its complement are equally likely, so each has probability 1/2.