Statistical Analysis with Excel® For Dummies®, 2nd Edition

Chapter 17. More on Probability

In This Chapter

• The beta version

• Pursuing Poisson

• Grappling with gamma

• Exponentially speaking

In the Chapter 16, 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 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.

Beta

This one connects with the binomial distribution, which I discuss in Chapter 16. 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 connection with the binomial 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, the random variable x