# Off the Number Line: Poisson Ivy

Interviewer:

Looks like you have a misspelling. Shouldn’t it be poison ivy?

Cartoonist:

That’s Poisson with English pronunciation pwass-ahn, as in “Poisson distribution”.

Interviewer:

What’s a Poisson distribution?

Cartoonist:

It’s an asymmetric bell-like curve used to model how many times one should expect an event to occur in a fixed time period assuming that the occurrences of these events are infrequent and independent from one another. The shape of the ivy on that wall is the shape of a Poisson distribution curve.

Interviewer:

Ah, now the cartoon makes sense. Can you give an example of when you would use a Poisson distribution?

Cartoonist:

Sure. I walk my son to school each morning and we occasionally see hummingbirds. We don’t see them every day, but on average, we see about 4 hummingbirds a week. Seeing a humming bird is an “event.” Since humming birds don’t fly in flocks, each sighting can be treated as an independent event. If you wanted to know the probability of seeing a given number of humming birds in a week, say 3 or 5, you can use a Poisson distribution with a mean of 4 to model that.

Interviewer:

Perfect. I get it now. So to connect this to the cartoon, you could also model the number of visitors to a park who contract a poison ivy rash each month.

Cartoonist:

Yes! That would be a good use case!

Interviewer:

I really do learn a lot from these Off the Number Line cartoons. Looking forward to what you have in store for next week!

Interested in challenging your math and problem-solving skills?

Matthew Peterson, Ph.D., is Co-founder and Chief Research & Development Officer at the MIND Research Institute. James Huang is Senior Visual Designer at MIND Research Institute.

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