Chapter 13: Inferential Statistics and Distributions
216
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.
4. Press
… |
to display the
STAT TESTS
menu,
and then press
†
until
8:TInterval
is highlighted.
5. 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
.
Press
†
y 9
and press
†
until
HGHT
is
highlighted and then press
Í
.
Press
† † Ë
99
to enter a 99 percent confidence
level at the
C-Level:
prompt.
6. 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.
