# 7: Confidence Intervals and Sample Size

- Page ID
- 10958

In this chapter, you will learn to construct and interpret confidence intervals. You will also learn a new distribution, the Student's-t, and how it is used with these intervals. Throughout the chapter, it is important to keep in mind that the confidence interval is a random variable. It is the population parameter that is fixed.

- 7.1: Confidence Intervals
- In this chapter, you will learn to construct and interpret confidence intervals. You will also learn a new distribution, the Student's-t, and how it is used with these intervals. Throughout the chapter, it is important to keep in mind that the confidence interval is a random variable. It is the population parameter that is fixed.

- 7.2: Confidence Intervals for the Mean with Known Standard Deviation
- A confidence interval for a population mean with a known standard deviation is based on the fact that the sample means follow an approximately normal distribution.

- 7.3: Confidence Intervals for the Mean with Unnown Standard Deviation
- We rarely know the population standard deviation. In the past, when the sample size was large, this did not present a problem to statisticians. They used the sample standard deviation ss as an estimate for σσ and proceeded as before to calculate a confidence interval with close enough results. However, statisticians ran into problems when the sample size was small. A small sample size caused inaccuracies in the confidence interval.

- 7.4: Confidence Intervals and Sample Size for Proportions
- The procedure to find the confidence interval, the sample size, the error bound, and the confidence level for a proportion is similar to that for the population mean, but the formulas are different.

- 7.5: Confidence Intervals (Summary)
- In this module, we learned how to calculate the confidence interval for a single population mean where the population standard deviation is known.

- 7.E: Confidence Intervals (Optional Exercises)
- These are homework exercises to accompany the Textmap created for "Introductory Statistics" by OpenStax.

## Contributors and Attributions

Barbara Illowsky and Susan Dean (De Anza College) with many other contributing authors. Content produced by OpenStax College is licensed under a Creative Commons Attribution License 4.0 license. Download for free at http://cnx.org/contents/30189442-699...b91b9de@18.114.