Excel 2000 in a Nutshell

Name

POISSON

Synopsis

Use POISSON to determine the poisson probabilities.

To Calculate

=POISSON(X, Mean, Cumulative)

All three of the arguments are required for this function.

X

Indicates a positive number that specifies the number of events. If X is not an integer value it is truncated.

Mean

Indicates a positive number that specifies the expected numeric value.

Cumulative

This argument must be a logical value of TRUE of FALSE that indicates the actual form of the function. If this argument is TRUE, the function returns the probability that the number of random events will be between 0 and the value specified for the X argument. If the value of this argument is FALSE, the function returns the probability that the number of events will be exactly the value specified for the X argument.

Example

Figure 15-37 illustrates how POISSON is used to determine the probability that the specified number of car accidents occurred yesterday when the average number of daily accidents for the year is 6. The first value indicates the probability that the number of accidents that occurred is between 0 and 10. The second value that is returned indicates the probability that exactly 10 accidents occurred yesterday. There are several important assumptions required before this distribution is used.

Figure 15-37. Use POISSON to determine the probability that the specified number of events occurred with a set ...