Syntax
POISSON.DIST(x, mean, cumulative)
| Parameter | Description |
|---|---|
| x | Parameter of the POISSON.DIST function. |
| mean | Parameter of the POISSON.DIST function. |
| cumulative | Parameter of the POISSON.DIST function. |
Examples
Exactly 3 support tickets in an hour
Formula
=POISSON.DIST(3, 5, FALSE)
Returns ~0.1404. If the average is 5 tickets/hour, the probability of getting exactly 3 in a given hour is about 14%.
At most 2 defects per unit
Formula
=POISSON.DIST(2, 4, TRUE)
Returns ~0.2381. With an average of 4 defects per unit, there is about a 23.8% chance of finding 2 or fewer defects.
Probability of zero accidents
Formula
=POISSON.DIST(0, 1.5, FALSE)
Returns ~0.2231. If a factory averages 1.5 accidents per month, there is about a 22.3% chance of a month with zero accidents.
Common Errors
#NUM!
x must be a non-negative integer (or will be truncated) and mean must be non-negative.
#VALUE!
Occurs when arguments are non-numeric.
Tips
Cumulative for 'at most' questions
Set cumulative=TRUE to answer 'what is the probability of x or fewer events?' Set FALSE for the probability of exactly x events.
Scale the mean for different intervals
If your rate is 10 events per day but you want the probability for a 3-day window, multiply the mean by 3 (use 30).
'More than' calculations
For P(X > k), calculate =1 - POISSON.DIST(k, mean, TRUE). For example, P(more than 5 calls) = 1 - POISSON.DIST(5, mean, TRUE).
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