A study was performed comparing different nonpharmacologic treatments for people with high normal diastolic blood pressure (DBP) (80-89mm Hg). One of the modes of treatment
studied was stress management. People were randomly assigned to a stress management intervention (SMI) and a control group. Participants randomized to SMI were given instruction in a group setting concerning different techniques for stress management.
Participants randomized to control were advised to pursue their normal lifestyles. Both groups were told that their blood pressure would be closely monitored and that their physician would be notified of any consistent elevation.
The results for the SMI group (n=242) at the end of the study (18 months) were as follows:
mean (change) = - 5.53 mm Hg (follow-up minus baseline)
sd (change) = 6.48 mm Hg
a. What test can be used to assess if mean blood pressure has changed significantly in the SMI group? Perform the test and report its result. The results for the control group (n=320) at the end of the study were as follows: mean (change) = - 4.77 mm Hg sd (change) = 6.09 mm Hg
b. What test can be used to compare mean blood-pressure change between the two groups? Perform the test and report its result.
c. The study team wondered whether the sample size in both groups was large enough to detect a true increased reduction of the mean DBP of at least 2mm Hg in the SMI intervention group over that in the control group, with a power of 90% and allowing a Type I error of at most 5%. Can you give an answer?