# Connexions

You are here: Home » Content » Confidence Intervals: Confidence Interval Lab III

### Recently Viewed

This feature requires Javascript to be enabled.

### Tags

(What is a tag?)

These tags come from the endorsement, affiliation, and other lenses that include this content.

# Confidence Intervals: Confidence Interval Lab III

Summary: Note: This module is currently under revision, and its content is subject to change. This module is being prepared as part of a statistics textbook that will be available for the Fall 2008 semester.

Note: You are viewing an old version of this document. The latest version is available here.

Class Time:

Names:

## Student Learning Outcomes:

• The student will calculate a 90% confidence interval using the given data.
• The student will examine the relationship between the confidence level and the percent of constructed intervals that contain the population average.

## Do the Experiment:

### Part I

 59.4 71.6 69.3 65 62.9 66.5 61.7 55.2 67.5 67.2 63.8 62.9 63 63.9 68.7 65.5 61.9 69.6 58.7 63.4 61.8 60.6 69.8 60 64.9 66.1 66.8 60.6 65.6 63.8 61.3 59.2 64.1 59.3 64.9 62.4 63.5 60.9 63.3 66.3 61.5 64.3 62.9 60.6 63.8 58.8 64.9 65.7 62.5 70.9 62.9 63.1 62.2 58.7 64.7 66 60.5 64.7 65.4 60.2 65 64.1 61.1 65.3 64.6 59.2 61.4 62 63.5 61.4 65.5 62.3 65.5 64.7 58.8 66.1 64.9 66.9 57.9 69.8 58.5 63.4 69.2 65.9 62.2 60 58.1 62.5 62.4 59.1 66.4 61.2 60.4 58.7 66.7 67.5 63.2 56.6 67.7 62.5

1. Listed above are the heights of 100 women. Use a random number generator to randomly select 10 data values.
2. Calculate the sample mean and sample standard deviation. Assume that the population standard deviation is known to be 3.3. With these values, construct a 90% confidence interval for your sample of 10 values. Write the confidence interval you obtained in the first space of the table below.
3. Now write your confidence interval on the board. As others in the class write their confidence intervals on the board, copy them into the table below:

### Part II

1. The actual population mean for the 100 heights given above is μ=63.4μ=63.4 size 12{μ="63" "." 4} {}. Using the class listing of confidence intervals, count how many of them contain the population mean μμ size 12{μ} {}; i.e., for how many intervals does the value of μμ size 12{μ} {} lie between the endpoints of the confidence interval?
2. Divide this number by the total number of confidence intervals generated by the class to determine the percent of confidence intervals that contain the mean μμ size 12{μ} {}. Write this percent below.
3. Is the percent of confidence intervals that contain the population mean μμ size 12{μ} {} close to 90%?
4. Suppose we had generated 100 confidence intervals. What do you think would happen to the percent of confidence intervals that contained the population mean?
5. When we construct a 90% confidence interval, we say that we are 90% confident that the true population mean lies within the confidence interval. Using complete sentences, explain what we mean by this phrase.
6. Some students think that a 90% confidence interval contains 90% of the data. Use the list of data given on the first page and count how many of the data values lie within the confidence interval that you generated on that page. How many of the 100 data values lie within your confidence interval? What percent is this? Is this percent close to 90%?
7. Explain why it does not make sense to count data values that lie in a confidence interval. Think about the random variable that is being used in the problem.
8. Suppose you obtained the heights of 10 women and calculated a confidence interval from this information. Without knowing the population mean μμ size 12{μ} {}, would you have any way of knowing for certain if your interval actually contained the value of μμ size 12{μ} {}? Explain.

** This lab was designed and contributed by Diane Mathios.

## Content actions

### Give feedback:

My Favorites (?)

'My Favorites' is a special kind of lens which you can use to bookmark modules and collections. 'My Favorites' can only be seen by you, and collections saved in 'My Favorites' can remember the last module you were on. You need an account to use 'My Favorites'.

| A lens I own (?)

#### Definition of a lens

##### Lenses

A lens is a custom view of the content in the repository. You can think of it as a fancy kind of list that will let you see content through the eyes of organizations and people you trust.

##### What is in a lens?

Lens makers point to materials (modules and collections), creating a guide that includes their own comments and descriptive tags about the content.

##### Who can create a lens?

Any individual member, a community, or a respected organization.

##### What are tags?

Tags are descriptors added by lens makers to help label content, attaching a vocabulary that is meaningful in the context of the lens.

| External bookmarks