In the past decade intensive antismoking campaigns have been sponsored by both federal and private agencies. Suppose the American Cancer Society randomly sampled 1,500 adults in 1989 and then sampled 2,000 adults in 1999 to determine whether there was evidence that the percentage of smokers had decreased. The results of the two independent sample surveys are shown in the following table.

a. Use the data in the table to estimate the true difference between the proportion of smokers for these two years. Use a 95% confidence interval.

• Step 1: Make sure that "Input" menu option is selected.
• Step 2: Type "1989" in the "Sample 1 Label" box and "1999" in the "Sample 2 Label" box.
• Step 3: Type "1500" in the "Sample 1 size" box and "2000" in the "Sample 2 size" box.
• Step 4: Type ".367" in the "Sample 1 proportion" box and ".326" in the "Sample 2 proportion" box.
• Step 5: Select the "Hypothesis test" from menu options.

The output will include: Sample sizes, Means, Proportions, Difference of proprtions, followed by a 95% confidence interval for the difference between population proportions.

b. Find a 99% confidence interval by following the steps given below:

• Step 1: Make sure that "Input" menu option is selected.
• Step 2: Type "1989" in the "Sample 1 Label" box and "1999" in the "Sample 2 Label" box.
• Step 3: Type "1500" in the "Sample 1 size" box and "2000" in the "Sample 2 size" box.
• Step 4: Type ".367" in the "Sample 1 proportion" box and ".326" in the "Sample 2 proportion" box.
• Step 5: Select the "Hypothesis test" from menu options.
• Step 6: Click on the "Options" button on the upper right hand side of the window.
• Step 7: Change only Alpha from 5.0 to 1.0.
• Step 8: Click on the "OK" button.

The output will include: Sample sizes, Means, Proportions, Difference of proprtions, followed by a 99% confidence interval for the difference between population proportions.

c. By using your answers to a and b, what can you say about the change in proportion of smokers from 1989 to 1999?