1. Flying J Diesel Fuel Prices Using Confidence Intervals to Estimate a Population Mean Susan and Cliff

2. Objectives What’s the difference between a 95% Confidence Interval and a 99% Confidence Interval for estimating a population mean? How does sample size influence both the 95% and 99% Confidence Interval for estimating a population mean?

3. Context With rising diesel fuel prices, how does a trucking company make a profit? Realistic estimates of the price of diesel fuel could be critically important

4. Population and Random Sampling Database of diesel fuel prices at 167 Flying J truck stops across the continental U.S. SPSS – Statistical Package for the Social Sciences Use SPSS to create 95% and 99% Confidence Intervals for various sample sizes (n = 10, n = 20, n = 50) Demonstrate rossman.chance.com Applet for Confidence Intervals

8. “Based on a sample of 10 cases, I am 95% confident that the population mean diesel fuel price is between $2.81 and $2.94”

10. “Based on a sample of 10 cases, I am 99% confident that the population mean diesel fuel price is between $2.78 and $2.97”

14. “Based on a sample of 10 cases, I am 95% confident that the population mean diesel fuel price is between $2.81 and $2.94” “Based on a sample of 10 cases, I am 99% confident that the population mean diesel fuel price is between $2.78 and $2.97”

15. “Based on a sample of 10 cases, I am 95% confident that the population mean diesel fuel price is between $2.81 and $2.94” “Based on a sample of 10 cases, I am 99% confident that the population mean diesel fuel price is between $2.78 and $2.97” “Based on a sample of 20 cases, I am 95% confident that the population mean diesel fuel price is between $2.84 and $2.95” “Based on a sample of 20 cases, I am 99% confident that the population mean diesel fuel price is between $2.82 and $2.98”

16. “Based on a sample of 10 cases, I am 95% confident that the population mean diesel fuel price is between $2.81 and $2.94” “Based on a sample of 10 cases, I am 99% confident that the population mean diesel fuel price is between $2.78 and $2.97” “Based on a sample of 20 cases, I am 95% confident that the population mean diesel fuel price is between $2.84 and $2.95” “Based on a sample of 20 cases, I am 99% confident that the population mean diesel fuel price is between $2.82 and $2.98” “Based on a sample of 50 cases, I am 95% confident that the population mean diesel fuel price is between $2.84 and $2.91” “Based on a sample of 50 cases, I am 99% confident that the population mean diesel fuel price is between $2.83 and $2.93”

17. Assessment Is a 95% confidence interval larger or smaller than a 99% confidence interval? As you increase sample size, both the 95% and the 99% confidence intervals become __________.

24. Caution Applet can be tricky!