To study whether or not pressure exerted on the upper arm increases bleeding time, 39 persons had their upper arm subjected to a pressure of 40 mmHg of mercury and their fingers pricked.
Their mean bleeding time was 2.192 min, and the standard deviation of their bleeding times was .765 min. Forty-three other persons acted as controls. No pressure was used for the controls, and their bleeding time was found to have a mean of 1.524 minutes and a standard deviation of .614min.
Give a 95% confidence interval for the difference in bleeding times. Do you think pressure increases mean bleeding time? Why?