Is red wine better than white wine? Observational studies suggest that moderate use of alcohol by adults reduces heart attacks and that red wine may have special benefits. One reason may be that red wine contains polyphenols, substances that do good things to cholesterol in the blood and so may reduce the risk of heart attacks. In an experiment, healthy men were assigned at random to drink half a bottle of either red or white wine each day for two weeks. The level of polyphenols in their blood was measured before and after the two-week period. Here are the percent changes in level for the subjects in both groups:28 Red wine: 3.5 8.1 7.4 4.0 0.7 4.9 8.4 7.0 5.5 White wine: 3.1 0.5 3.8 4.1 0.6 2.7 1.9 5.9 0.1

(b) Construct and interpret a 90% confidence interval for the difference in mean percent change in polyphenol levels for the red wine and white wine treatments.

(c) Does the interval in part (b) suggest that red wine is more effective than white wine? Explain.