Card 3 / 10: Use the following information for questions 1-3: In a cohort study of breast cancer in older women, there are two groups, those who were exposed to a known carcinogen and those who were not.In the unexposed group, the mean systolic blood pressure was 105 mm Hg, with a standard deviation of 12 mm Hg. The sample size of the unexposed group was 196. What is the 95% confidence interval for the mean systolic blood pressure of this group?
Answer:
First, find the standard error: = Standard deviation / sqrt(N) = 12 / sqrt(196) = 12/14 = 0.857 Then, calculate the confidence intervals: 95% CI = mean + 1.96*SE = 105 + 1.96*0.857 = 105 + 1.68 = (103.3, 106.7)
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Epidemiology Sampling & Confidence Intervals
Author:
Dr.Janet ForresterProfessor
Tufts University School of Medicine
USA
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