Operation Manual

Chapter 13: Inferential Statistics and Distributions 223
Interpreting the results
The first line, (159.74,173.94), shows that the 99 percent confidence interval for the population mean is
between about 159.74 centimeters and 173.94 centimeters. This is about a 14.2 centimeters spread.
The .99 confidence level indicates that in a very large number of samples, we expect 99 percent of the
intervals calculated to contain the population mean. The actual mean of the population sampled is
165.1 centimeters, which is in the calculated interval.
The second line gives the mean height of the sample v used to compute this interval. The third line
gives the sample standard deviation
Sx. The bottom line gives the sample size n.
To obtain a more precise bound on the population mean m of women’s heights, increase the sample size
to 90. Use a sample mean v of 163.8 and sample standard deviation
Sx of 7.1 calculated from the larger
random sample. This time, use the Stats (summary statistics) input option.
7. Press … | to display the
STAT TESTS menu, and
then press † until
8:TInterval is highlighted.
8. Press Í to select
8:TInterval. The inferential
stat editor for
TInterval is displayed. If Data is not
selected for Inpt:, press | Í to select Data.
9. Press † y 9 and press † until HGHT is
highlighted and then press Í.
10. Press † † Ë 99 to enter a 99 percent confidence
level at the C-Level: prompt.
11. Press † to move the cursor onto
Calculate, and
then press Í. The confidence interval is
calculated, and the
TInterval results are displayed
on the home screen.
1. Press … |
8 to display the inferential stat editor
for
TInterval.
Press ~ Í to select
Inpt:Stats. The editor
changes so that you can enter summary statistics as
input.
2. Press †
163 Ë 8 Í to store 163.8 to v.
Press 7 Ë 1 Í to store 7.1 to Sx.
Press
90 Í to store 90 to n.