Statistics All-in-One For Dummies

Chapter 14

Confidence Intervals: Making Your Best Guesstimate

IN THIS CHAPTER

Understanding confidence interval pieces, parts, and interpretation

Calculating with confidence

Examining factors that influence the width of a confidence interval

Detecting misleading results

Most statistics are used to estimate some characteristic about a population of interest, such as average household income, the percentage of people who buy birthday gifts online, or the average amount of ice cream consumed in the United States every year (and the resulting average weight gain — nah!). Such characteristics of a population are called parameters. Typically, people want to estimate (take a good guess at) the value of a parameter by taking a sample from the population and using statistics from the sample that will give them a good estimate. The question is: How do you define “good estimate”?

As long as the process is done correctly (and in the media, it often isn’t!), an estimate can often get very close to the parameter. This chapter gives you an overview of confidence intervals (the type of estimates ...