11. Dernellis and Panaretou examined subjects with hypertension and healthy control subjects. One of the variables of interest was the aortic stiffness index. Measures of this variable were calculated from the aortic diameter evaluated by M-mode echocardiography and blood pressure measured by a sphygmomanometer. Generally, physicians wish to educe aortic stiffness. In the 15 patients with hypertension (group 1), the mean aortic stiffness index was 19.16 with a standard deviation of 5.29. In the 30 control subjects (group 2), the mean aortic stiffness index was 9.53 with a standard deviation of 2.69. We wish to determine if the two populations represented by these samples differ with respect to mean aortic stiffness index.