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Chapter 11: Statistical Inference: One-Sample Confidence Interval Looking Ahead: What Is This Chapter About? A sample mean is often used to estimate a population mean when it is not possible to observe all of the elements in the population. Unfortunately, sample means vary from one random sample to the next. Hence, the mean of a particular sample is unlikely to equal the population mean. In this chapter you will learn how to find a range of values called a confidence interval that is likely to include the unknown population mean. Confidence intervals are not used as much as null hypothesis significance tests in the behavioral sciences, health sciences, and education. This is true even though confidence intervals are more informative. The American Psychological Association (2001, p. 22) recommends that researchers make greater use of confidence interval procedures. Because of this recommendation, the use of confidence intervals in psychology will likely increase. After reading this chapter, you should know the following: ■ Four common criticisms of null hypothesis significance testing ■ How to use the t sampling distribution to construct a confidence interval for a population mean ■ When and how to use one- and two-sided confidence intervals ■ How Hedges’s g statistic can help you assess practical significance ■ The advantages of confidence intervals over null hypothesis significance tests