The Poisson Distribution

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Hook

Counting the unexpected

How many emails will land in your inbox this hour? How many cars will pass a quiet junction in a minute? How many calls hit a help desk before lunch? Each event is unpredictable on its own, yet the count over an interval follows a beautifully simple law — the Poisson distribution — controlled by just one number: the average rate λ.

Poisson models the count of rare, independent events in a fixed interval. The single parameter λ is the mean count.

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