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The likelihood of an event (outcome) is the chance that someone will experience that event; i.e. the number of people in a group that experience the event during a specified period, divided by the total number of people in that group.
The event can be either an undesirable or a desirable outcome.
For example, if 5 out of 100 people who had a heart attack had a second heart attack during the next 4 years, the likelihood of a second heart attack is 5/100 or 5%. Conversely, the likelihood of not having a second heart attack is 95/100 or 95%.
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