A​ 99% confidence level requires __?___ subjects. (Round to the nearest subject)

Question

A doctor wants to estimate the mean HDL cholesterol of all​ 20- to​ 29-year-old females. How many subjects are needed to estimate the mean HDL cholesterol within 3 points with 99% confidence assuming s=19.5 based on earlier​ studies? Suppose the doctor would be content with 90% confidence. How does the decrease in confidence affect the sample size​ required?

A​ 99% confidence level requires __?___ subjects. (Round to the nearest subject)

Answer 1

sample size (n) = (z alpha/2 * s/E)^2

z alpha/2 = z for 0.995 probability = 2.58

s = 19.5

E = 3

plug values into sample size (n) equation and compute

Decrease in confidence reduces sample size required because z alpha/2 is 1.645