A doctor wants to estimate the mean HDL cholesterol of all 20- to 29-year-old fe

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

2 points with 99 % confidence assuming S= 12.6 based on earlier studies?

Suppose the doctor would be content with 95 % confidence. How does the decrease in confidence affect the sample size required?

- A 99% confidence level requires _______subjects. (Round up to the nearest subject.)

- Therefore, a 99% confidence level with a margin of error of 2 points requires _________ subjects.

Explanation / Answer

A doctor wants to estimate the HDL cholesterol of all 20- to 29-year-old females. How many subjects are needed to estimate the mean HDL cholesterol within 2 points with 99 % confidence assuming S= 12.6 based on earlier studies?

s = 12.6

E = 2

n = ((z*s)/E)^2

z value for 99 % CI = 2.5758

n = ((2.5758*12.6) / 2)^2

n = 263

Suppose the doctor would be content with 95 % confidence. How does the decrease in confidence affect the sample size required?

z-value for a 95 % CI = 1.96

n = (1.96*12.6/2)^2 = 152

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