Chapter 3

Getting Statistical: A Short Review of Basic

Statistics

IN THIS CHAPTER

Getting a handle on probability, randomness, sampling, and inference

Tackling hypothesis testing

Understanding nonparametric statistical tests

This chapter provides an overview of basic concepts often taught in a one-term introductory statistics

course. These concepts form a conceptual framework for the topics that we cover in greater depth

throughout this book. Here, you get the scoop on probability, randomness, populations, samples,

statistical inference, hypothesis testing, and nonparametric statistics.

Note: We only introduce the concepts here. They’re covered in much greater depth in Statistics For

Dummies and Statistics II For Dummies, both written by Deborah J. Rumsey, PhD, and published by

Wiley. Before you proceed, you may want to skim through this chapter to review the topics we cover

so you can fill any gaps in your knowledge you may need in order to understand the concepts we

introduce.

Taking a Chance on Probability

Defining probability is hard to do without using another word that means the same thing (or almost the

same thing). Probability is the degree of certainty, the chance, or the likelihood that an event will

occur. Unfortunately, if you then try to define chance or likelihood or certainty, you may wind up using

the word probability in the definition. No worries — we clear up the basics of probability in the

following sections. We explain how to define probability as a number and provide a few simple rules

of probability. We also define odds, and compare odds to probability (because they are not the same

thing).

Thinking of probability as a number

Probability describes the relative frequency of the occurrence of a particular event, such as getting

heads on a coin flip or drawing the ace of spades from a deck of cards. Probability is a number

between 0 and 1, although in casual conversation, you often see probabilities expressed as

percentages. Probabilities are usually followed by the word chance instead of probability. For

example: If the probability of rain is 0.7, you may hear someone say that there’s a 70 percent chance of

rain.