we wish to design a study to assess risk factors for stroke and dementia. there are two primary outcome measures. the first is a measure of neurological function. patients with "normal" function typically score 70 with a standard deviation of 15. the second outcome is incident stroke. in patients over the age of 65 approximately 14% develop stroke over 25 years. how many participants over the age of 65 must be enrolled to ensure the following?
A. That the margin of error in a 95 % confidence interval for the difference in mean neurologic function scores between men and women does not exceed 2 units.
B. That we have 80% power to detect a 20% reduction in incidence of stroke between participants who participate in a healthy aging program as compared to those who do not. assume that the incidence of stroke is 14% in those who do not participate. Assume the incidence is 14% in group who do not participate and 20% lower (i.e 11.2%) in the group who participate.