How to Calculate Poisson Probability
What is Poisson Probability?
Poisson distribution models the number of events in a fixed interval when events occur independently at a constant average rate. Used for rare event probability.
Formula
P(X = k) = (λᵏ × e⁻λ) / k! where λ is the average rate
Step-by-Step Guide
- 1Enter λ (average number of events)
- 2Enter k (number of events of interest)
- 3Calculate using the Poisson formula
Worked Examples
Input
λ = 3, k = 2
Result
P(X = 2) ≈ 0.224
(3² × e⁻³) / 2! ≈ 0.224
Common Mistakes to Avoid
- ✕Confusing λ with the event value
- ✕Using Poisson when binomial is more appropriate
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