# Class 25: Topic 19: Confidence Intervals: Means

Back to Pause for Breath. On to About the Projects.

This outline is also available in PDF.

Held: Wednesday, 2 April 2008

Summary: We return to the computation of confidence intervals, this time using quantitative data (represented by the sample mean, rather than the sample proportion). Along the way, we consider the effects of computing the standard deviation of the sampling population using the sample's standard deviation, rather than the population's standard deviation.

Notes:

• I will continue to reserve time at the start of class for any campus issues you would like to discuss.
• If you did not turn in Topic 18 on Monday, please turn it in today.
• I have a tentative updated schedule for the next few weeks. I'm still working to coordinate with the faculty in the other two sections.
• Work for Friday: Activities 19-7, 19-12, 19-13, 19-19, 19-22.
• I will provide you with one page of notes for next week's exam. You can help control what's on the exam by providing me with your preferences for the contents of those notes by Monday's class. I will not explain symbols in the notes, but I am happy to include formulae. (I'll distribute the notes on Monday.)
• Because we'll be discussing projects on Friday, there is no additional preparation necessary for Friday's class.

Overview:

• Quick review of confidence intervals.
• Confidence Intervals, Revisited.

## Confidence Intervals, Revisited

As you know from much of the rest of this text, our authors like to alternate between doing a topic for categorical data and then return to the topic again using quantitative data.

• Today, we consider confidence intervals for sample means (instead of for sample proportions).
• Wednesday, we consider tests of significance for sample means.

In considering confidence intervals for sample means, we'll ask the same questions we asked about confidence intervals for sample proportions.

• What is the critical value, t*?
• What formula do we use for the CI?
• How do we determine the critical value?

Back to Pause for Breath. On to About the Projects.

Disclaimer: I usually create these pages on the fly, which means that I rarely proofread them and they may contain bad grammar and incorrect details. It also means that I tend to update them regularly (see the history for more details). Feel free to contact me with any suggestions for changes.

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Samuel A. Rebelsky, rebelsky@grinnell.edu

Copyright © 2008 Samuel A. Rebelsky. This work is licensed under a Creative Commons Attribution-NonCommercial 2.5 License. To view a copy of this license, visit `http://creativecommons.org/licenses/by-nc/2.5/` or send a letter to Creative Commons, 543 Howard Street, 5th Floor, San Francisco, California, 94105, USA.