Confidence Intervals and Sample Size
Confidence Intervals and Sample Size
Confidence Intervals and Sample Size
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lu49076_ch07.qxd 5/20/2003 3:16 PM Page 346<br />
346 Chapter 7 <strong>Confidence</strong> <strong>Intervals</strong> <strong>and</strong> <strong>Sample</strong> <strong>Size</strong><br />
TI-83 Plus<br />
Step by Step<br />
Excel<br />
Step by Step<br />
7–4<br />
<strong>Confidence</strong> <strong>Intervals</strong><br />
<strong>and</strong> <strong>Sample</strong> <strong>Size</strong> for<br />
Proportions<br />
7–22<br />
One-<strong>Sample</strong> T: HomeFires<br />
Variable N Mean StDev SE Mean 99% CI<br />
HomeFires 7 7041.43 1610.27 608.63 (4784.99, 9297.87)<br />
Finding a t <strong>Confidence</strong> Interval for the Mean (Data)<br />
1. Enter the data into L 1.<br />
2. Press STAT <strong>and</strong> move the cursor to TESTS.<br />
3. Press 8 for TInterval.<br />
4. Move the cursor to Data <strong>and</strong> press ENTER.<br />
5. Type in the appropriate values.<br />
6. Move the cursor to Calculate <strong>and</strong> press ENTER.<br />
Finding a t <strong>Confidence</strong> Interval for the Mean (Statistics)<br />
1. Press STAT <strong>and</strong> move the cursor to TESTS.<br />
2. Press 8 for TInterval.<br />
3. Move the cursor to Stats <strong>and</strong> press ENTER.<br />
4. Type in the appropriate values.<br />
5. Move the cursor to Calculate <strong>and</strong> press ENTER.<br />
Finding a t <strong>Confidence</strong> Interval for the Mean<br />
Excel has a procedure to produce the maximum error of the estimate. But it does not produce confidence<br />
intervals. However, you may determine confidence intervals for the mean by using the<br />
Mega-Stat Add-in available on your CD <strong>and</strong> Online Learning Center. If you have not installed this<br />
add-in, do so by following the instructions on page 24.<br />
Find the 95% confidence interval, using this sample:<br />
625 675 535 406 512 680 483 522 619 575<br />
1. From the toolbar, select Mega-Stat><strong>Confidence</strong> <strong>Intervals</strong>/<strong>Sample</strong> <strong>Size</strong>.<br />
2. In the dialog box, select the <strong>Confidence</strong> interval mean tab.<br />
3. Enter 563.2 for the mean of the data, <strong>and</strong> then select t. Enter 87.9 for the st<strong>and</strong>ard deviation<br />
<strong>and</strong> 10 for n, the sample size.<br />
4. Either type in or scroll to 95% for the confidence level, <strong>and</strong> then click [OK].<br />
The result of the procedure will show the output in a new chart as indicated below.<br />
<strong>Confidence</strong> interval - mean<br />
95% confidence level<br />
563.2 mean<br />
87.9 std. dev.<br />
10 n<br />
2.262 t (df � 9)<br />
62.880 half-width<br />
626.080 upper confidence limit<br />
500.320 lower confidence limit<br />
A USA TODAY Snapshots feature stated that 12% of the pleasure boats in the United<br />
States were named Serenity. The parameter 12% is called a proportion. It means that of<br />
all the pleasure boats in the United States, 12 out of every 100 are named Serenity. A proportion<br />
represents a part of a whole. It can be expressed as a fraction, decimal, or per-<br />
12 3<br />
centage. In this case, 12% � 0.12 � or . Proportions can also represent probabilities.<br />
100<br />
25
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