A recent study1 examines chocolate’s effects on blood vessel function in healthy people. In the randomized, double-blind, placebo-controlled study, 11 people received 46 grams (1.6 ounces) of dark chocolate (which is naturally flavonoid-rich) every day for two weeks, while a control group of 10 people received a placebo consisting of dark chocolate with low flavonoid content. Participants had their vascular health measured (by means of flow-mediated dilation) before and after the two-week study. The increase over the two-week period was measured, with larger numbers indicating greater vascular health. For the group getting the good dark chocolate, the mean increase was 1.3 with a standard deviation of 2.32, while the control group had a mean change of -0.96 with a standard deviation of 1.58.
Find a 90% confidence interval for the difference in means between the two groups MC-MN , where MC represents the mean increase in flow-mediated dilation for people eating dark chocolate every day and MN represents the mean increase in flow-mediated dilation for people eating a dark chocolate substitute each day. You may assume that neither sample shows significant departures from normality.
Round your answers to two decimal places.