The Poisson distribution is discrete. It describes the number of times an event occurs in a given interval (usually time), such as the number of telephone calls per minute, the number of errors per page in a document, or the number of defects per 100 yards of material.
Parameter
Rate
Conditions
The Poisson distribution is used under these conditions:
Number of possible occurrences is not limited.
Occurrences are independent.
Average number of occurrences is the same from unit to unit.