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We need to find the confidence interval for the SLEEP variable.To do this, we need to find the mean and standard deviation withthe Week 1 spreadsheet. Then we can the Week 5 spreadsheet to findthe confidence interval.

First, find the mean and standard deviation by copying the SLEEPvariable and pasting it into the Week 1 spreadsheet. Write down themean and the sample standard deviation as well as the count. Openthe Week 5 spreadsheet and type in the values needed in the greencells at the top. The confidence interval is shown in the yellowcells as the lower limit and the upper limit.

1. Give and interpret the 95% confidence interval for the hoursof sleep a student gets. Change the confidence level to 99% to findthe 99% confidence interval for the SLEEP variable.

2. Give and interpret the 99% confidence interval for the hoursof sleep a student gets.

3. Compare the 95% and 99% confidence intervals for the hours ofsleep a student gets. Explain the difference between theseintervals and why this difference occurs.

In the Week 2 Lab, you found the mean and the standard deviationfor the HEIGHT variable for both males and females. Use thosevalues for follow these directions to calculate the numbersagain.

(From Week 2 Lab: Calculate descriptive statistics for thevariable Height by Gender. Click on Insert and then Pivot Table.Click in the top box and select all the data (including labels)from Height through Gender. Also click on “new worksheet” and thenOK. On the right of the new sheet, click on Height and Gender,making sure that Gender is in the Rows box and Height is in theValues box. Click on the down arrow next to Height in the Valuesbox and select Value Field Settings. In the pop up box, clickAverage then OK. Write these down.

Then click on the down arrow next to Height in the Values boxagain and select Value Field Settings. In the pop up box, click onStdDev then OK. Write these values down.)

You will also need the number of males and the number of femalesin the dataset. You can either use the same pivot table createdabove by selecting Count in the Value Field Settings, or you canactually count in the dataset. Then use the Week 5 spreadsheet tocalculate the following confidence intervals. The male confidenceinterval would be one calculation in the spreadsheet and thefemales would be a second calculation.

4. Give and interpret the 95% confidence intervals for males andfemales on the HEIGHT variable. Which is wider and why?

5. Give and interpret the 99% confidence intervals for males andfemales on the HEIGHT variable. Which is wider and why?

6. Find the mean and standard deviation of the DRIVE variable bycopying that variable into the Week 1 spreadsheet. Use the Week 4spreadsheet to determine the percentage of data points from thatdata set that we would expect to be less than 40. To find theactual percentage in the dataset, sort the DRIVE variable and counthow many of the data points are less than 40 out of the total 35data points. That is the actual percentage. How does this comparewith your prediction? Mean ______________ Standard deviation____________________ Predicted percentage______________________________ Actual percentage_____________________________ Comparison_________________________________________________________________________________________________________________

7. What percentage of data would you predict would be between 40and 70 and what percentage would you predict would be more than 70miles? Use the Week 4 spreadsheet again to find the percentage ofthe data set we expect to have values between 40 and 70 as well asfor more than 70. Now determine the percentage of data points inthe dataset that fall within this range, using same strategy asabove for counting data points in the data set. How do each ofthese compare with your prediction and why is there a difference?Predicted percentage between 40 and 70______________________________ Actual percentage_____________________________________________ Predicted percentagemore than 70 miles ________________________________ Actualpercentage ___________________________________________ Comparison___________________________________________________________________________________________________________________Why? __________________________________________________________________________________________________________________________

Sleep (hours)
7
7
5
7
6
8
7
8
5
8
8
4
8
8
6
8
8
8
7
10
6
7
8
5
8
7
7
4
9
8
7
7
8
8
10

Height (inches)
61
62
63
63
64
65
65
66
66
67
67
67
67
68
68
69
69
69
69
69
69
69
70
70
70
70
70
71
71
71
73
73
74
74
75