Poisson Distribution

Poisson Distribution

ST-03
ASPCSPAdvanced

Formula
P(r,t) = e^(−λt) × (λt)^r ÷ r!
When to Use

Calculate probability of rare, independent events occurring in a fixed interval. Used for incident rate prediction.

Symbol Legend
SymbolMeaningUnitNote
PProbability of r events occurring )decimal (0 to 1
rNumber of events of interest
λExpected event ratebaseline
tTime intervalsame units as λ
eNatural log base2.718

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