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 2-week period. Here are the percent changes in polyphenols for the subjects in each group:

a. A dotplot of the data is shown, along with summary statistics. Write a few sentences comparing the distributions.

b. Construct and interpret a 90% confidence interval for the difference in true mean percent change in polyphenol levels for healthy men like the ones in this study when drinking red wine versus white wine.

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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