Using the TI-83 calculator for Confidence Intervals about the mean (large samples n > 30)
Doing a confidence interval on the TI-83 is so easy you will never want to do one by hand (but should anyway!). Remember there are two situations you encounter when dealing with confidence intervals:
- Confidence intervals when you do not have the raw data, but do have the summary statistics (mena, standard deviation, etc..)
- Confidence intervals when you have the raw data
Consider the examples below:
- Suppose we sample n = 100 waist sizes of adult men and find
and 
. At the 95% degree of confidence find a confidence interval for the mean
First you should hit STAT, and highlight the TESTS submenu. Your calculator screen should look as follows:
Now select 7 for Zinterval, your screen should be as follows (Your data may be different):
Make sure Stats is highlighted, if it is not, use the arrow keys to highlight it and hit enter! Now use the arrow keys to move down and enter the standard deviation, the mean, the sample size and the confidence level, after you are done your screen should look as follows:
Now highlight the word Calculate and hit enter . Did you get this answer?
- You wish to estimate the average G.P.A. of Casper College students, so you take a random sample of 45 students and find their mean G.P.A. is 2.75 with a standard deviation of s = 0.94. Find a confidence interval at the 99% confidence level
The procedure is exactly the same as above, but different values to enter of course. First STAT, TESTS and then Zinterval to get the entry screen. After this enter the mean, standard deviation, sample size and level of confidence. Your screen should look as follows:
Now hit enter to calculate the answer - here it is!
- #20 on page 303
Once again the procedure is the same here are the final two screens - do these match your results?
4) Consider the following data of sample heights:
|
66.71 |
65.11 |
60.45 |
61.12 |
72.01 |
64.32 |
61.94 |
69.88 |
68.34 |
70.05 |
|
69.84 |
62.54 |
65.49 |
72.14 |
70 |
64.31 |
71.19 |
69.45 |
62.5 |
70.95 |
|
66.05 |
72.48 |
65.11 |
63.85 |
66.92 |
63.75 |
68.40 |
64.21 |
61.74 |
69.5 |
|
62.85 |
59.84 |
|
|
|
|
|
|
|
|
Find a 90% confidence interval for the mean using this data
My suggestions here are to do the following
- STAT edit to enter the data in a list (you choose)
- STAT CALC 1 Var Stats to calculate the mean and standard deviation of the data
- Enter The STAT TESTS menu as before, BUT THIS TIME use the arrow keys to highlight the word Data and hit enter
Your screen should look like the following screen:
Now You can hit VARS - then 5 for statistics to get the statistics variable menu to enter the 
symbol for the standard deviation. Also make sure you have the correct list entered and the appropriate confidence level. Here is the screen I have at this point:
Now calculate to get the final answer:
