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.

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

  

1. Give and interpret the 95% confidence interval for the hours ofsleep a student gets.
2. Give and interpret the 99% confidence interval for the hours ofsleep 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.

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

(From Week 2 Lab: Calculate descriptive statistics for thevariable Height by Gender. Click on Insert andthen Pivot Table. Click in the top box and selectall the data (including labels) from Heightthrough Gender. Also click on “new worksheet” andthen OK. On the right of the new sheet, click onHeight and Gender, making surethat Gender is in the Rows boxand Height is in the Valuesbox.   Click on the down arrow next toHeight in the Values box andselect Value Field Settings. In the pop up box,click Average then OK. Writethese down. Then click on the down arrow next toHeight in the Values box againand select Value Field Settings. In the pop upbox, click on StdDev 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 ValueField Settings, or you can actually count in thedataset.

Then use the Week 5 spreadsheet to calculate the followingconfidence intervals. The male confidence interval would be onecalculation in the spreadsheet and the females would be a secondcalculation.

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

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

3. 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___________________________________________________ ______________________________________________________________

4. 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 adifference?

Predicted percentage between 40 and 70______________________________ Actual percentage_____________________________________________ Predicted percentage more than 70 miles________________________________ Actual percentage___________________________________________ Comparison____________________________________________________ _______________________________________________________________ Why?__________________________________________________________ ________________________________________________________________