Statistics Workbook For Dummies with Online Practice, 2nd Edition

Chapter 5

Understanding Probability Basics

IN THIS CHAPTER

Warming up to probability rules and concepts

Steering clear of probability misconceptions

Forecasting the future with probabilities

In this chapter, you practice using and applying the rules and ideas of probability. The rules and laws of probability often go against our intuition. For example, a combination like 1, 2, 3, 4, 5, 6 seems a very unlikely winner in the lottery, when, in fact, it has just the same chance as any other combination (which shows how unlikely they all really are). And it might seem that a couple that has three girls in a row should have a much higher chance of having a boy this time, but barring any genetic predisposition to girls, the chance is still 50-50 each time. The practice in interpreting probability that this chapter provides helps ease your statistical state of mind and allows you to avoid making some of the more common misconceptions about the subject.

Grasping the Rules of Probability

The definition of the probability of an outcome is the long-run percentage (or relative frequency) of times that you expect the outcome to occur. Probabilities follow certain rules. Here they are in a ...