A study was performed comparing different nonpharmacologic treatments for people with high-normal diastolic blood pressure (DBP) (80-89 mm Hg). One of the modes of treatment studied was stress management. People were randomly assigned to a stress management intervention (SMI) group or a control group. Participants randomized to SMI were given instructions in a group setting conserning different techniques for stress management and met periodically over a 1-month period. Participants randomized to the control group were advised to pursue their normal lifestyles and 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) =−5.53mm Hg (follow-up - baseline), sd (change) =6.48mm Hg. How much power did the study have for detecting a significant difference between groups (using a two-sided test with a 5% level of significance) if the true effect of the SMI intervention is to reduce mean DBP by 2mm Hg more than the control group and the standard deviation of change within a group is 6mm Hg?

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A study was performed comparing different nonpharmacologic treatments for people with high-normal diastolic blood pressure (DBP) (80-89 mm Hg). One of the modes of treatment studied was stress management. People were randomly assigned to a stress management intervention (SMI) group or a control group. Participants randomized to SMI were given instructions in a group setting conserning different techniques for stress management and met periodically over a 1-month period. Participants randomized to the control group were advised to pursue their normal lifestyles and 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) =−5.53mm Hg (follow-up - baseline), sd (change) =6.48mm Hg.  How much power did the study have for detecting a significant difference between groups (using a two-sided test with a 5% level of significance) if the true effect of the SMI intervention is to reduce mean DBP by 2mm Hg more than the control group and the standard deviation of change within a group is 6mm Hg?

Nichole Watt · Accepted Answer

From the &quot;Table 3-The normal distribution&quot; in Appendix, the value of z0.975 is 1.96.  The value of power is obtained below:  Power =ϕ(−z1−a2+(|μ2−μ1|)σ12n1+σ22n2)  =ϕ(−1.96+(2)62242+62320)  =ϕ(1.953) [Use Table 3 - The normal distribution&quot; in Appendix]  =0.975  Thus, the value of power is 0.975.

A study was performed comparing different nonpharmacologic treatments for people

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