Question

9.2.8) A doctor wants to estimate the mean HDL cholesterol of 2229 year old females. How many subjects needed to estimate the mean HDL cholesterol with 2. 29% confidence assuming s equals 15. 6 based on there earlier studies? Suppose the doctor would be content with 95% confidence. How does the decrease in confidence affect the sample size required?

Answer 1

we have z score = 2.576 for 99% confidence interval, s = 15.6 and margin of error = 2

Using the formula, sample size = ((z*s)/ME)^2

setting the values, we get

sample size = ((2.576*15.6)/2)^2 = (40.1856/2)^2 = 403.72 or 404

so, a sample of 404 is required

Again using 95% confidence

we have z score = 1.96 for 99% confidence interval, s = 15.6 and margin of error = 2

Using the formula, sample size = ((z*s)/ME)^2

setting the values, we get

sample size = ((1.96*15.6)/2)^2 = (30.576/2)^2 = 233.72 or 234

so, a sample of 234 is required

Decrease in confidence level results in decreased sample size