Statistics Workbook For Dummies with Online Practice, 2nd Edition

Chapter 11

Calculating Confidence Intervals

IN THIS CHAPTER

Assembling the basic parts of a confidence interval

Calculating confidence intervals for one and two means and proportions

Knowing which confidence interval to use

Interpreting confidence intervals correctly

Introductory statistics looks at confidence intervals for means and proportions, from one or two populations. You use a confidence interval to find the population parameter (the population mean, the proportion in the population with a certain characteristic, and so on). In other words, you want to make a good guess, or a good estimate, as to what that population value is. You don’t use a confidence interval if you already have a claim or idea about what the population value is to test that claim. That situation calls for a hypothesis test (see Chapter 13).

Walking through a Confidence Interval

All confidence intervals contain the same basic parts: a sample statistic, plus or minus a margin of error. The margin of error measures how much you expect the sample statistic to vary from one sample to the next (see Chapter ...