Chapter 19

# More on Probability

IN THIS CHAPTER

Understanding the beta version

Pursuing Poisson

Grappling with gamma

Speaking exponentially

In Chapter 18, I delve into probability in a semiformal way, and introduce distributions of random variables. The binomial distribution is the starting point. In this chapter, I examine additional distributions.

One of the symbols on the pages of this book (and other books in the *For Dummies* series) lets you know that “technical stuff” follows. It might have been a good idea to hang that symbol above this chapter’s title. So here’s a small note of caution: Some mathematics follows. I put the math in to help you understand what you’re doing when you work with the dialog boxes of the Excel functions I describe.

Are these functions on the esoteric side? Well … yes. Will you ever have occasion to use them? Well … you just might.

## Discovering Beta

The beta distribution (not to be confused with *beta,* the probability of a Type 2 error) is a sort of chameleon in the world of distributions. It takes on a wide variety of appearances, depending on the circumstances. I won’t give you all the mathematics behind the beta distribution, because the full treatment involves calculus.

The beta distribution connects with the binomial distribution, which I discuss in Chapter 18. The connection is this: In the binomial, the random variable *x* is the number of successes in *N* trials with *p* as the probability of a success. *N* and *p* are constants. In the beta distribution, ...

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