Becoming a Data Head

CHAPTER 6Examine the Probabilities

Many people's notion of probability is so impoverished that it admits [one] of only two values: 50-50 and 99%, tossup or essentially certain.”

—John Allen Paulos, mathematician and author of “Innumeracy: Mathematical Illiteracy and Its Consequences”¹

Let's talk about probability—the language of uncertainty—and rekindle the conversation we started in Chapter 3, “Prepare to Think Statistically.” To recap, there's variation in all things; variation creates uncertainty; and probability and statistics are tools to help us manage uncertainty.

Our all-too-brief section on probability ended with a message: be mindful and recognize that your intuition can play tricks on you.

A fair statement, but such topics like probability deserve more than a bumper sticker warning. Complete understanding, if there is such a thing, requires reading massive textbooks, listening to long lectures, and a lifetime of study and debate. Even then, experts disagree on the interpretation and philosophy of probability.² You might not have the time or desire for that level of discussion (neither do we), so we'll spare you those debates and keep the focus on what you need to know to keep your intuition sharp and be successful in your work.

Our goal in this chapter, then, is to move you beyond a bumper sticker grasp of probability and to teach you some of its language, notation, tools, and traps. By the end of this chapter, you will be able to think and speak about probabilities ...