Head First Statistics

Chapter 7. Geometric, Binomial, and Poisson Distributions: Keeping Things Discrete

Calculating probability distributions takes time.

So far we’ve looked at how to calculate and use probability distributions, but wouldn’t it be nice to have something easier to work with, or just quicker to calculate? In this chapter, we’ll show you some special probability distributions that follow very definite patterns. Once you know these patterns, you’ll be able to use them to calculate probabilities, expectations, and variances in record time. Read on, and we’ll introduce you to the geometric, binomial and Poisson distributions.

Meet Chad, the hapless snowboarder

Chad likes to snowboard, but he’s accident-prone. If there’s a lone tree on the slopes, you can guarantee it will be right in his path. Chad wishes he didn’t keep hitting trees and falling over; his insurance is costing him a fortune.

There’s a lot riding on Chad’s performance on the slopes: his ego, his success with the ski bunnies on the trail, his insurance premiums. If it’s likely he’ll make it down the slopes in less than 10 tries, he’s willing to risk embarrassment, broken bones, and a high insurance deductible to try out some new snowboarding ...