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=14.6

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

nothing

subjects. (Round up to the nearest subject.)A

95%

confidence level requires

nothing

subjects. (Round up to the nearest subject.)

How does the decrease in confidence affect the sample size required?

A.

The sample size is the same for all levels of confidence.

B.

Decreasing the confidence level decreases the sample size needed.

C.

Decreasing the confidence level increases the sample size needed.

Explanation / Answer

for 99% confidence level ; z=2.5758

therefore for 99% required sample size =(z*std deviation/E)2 =354

for 95% confidence level ; z=1.96

therefore for 95% required sample size =(z*std deviation/E)2 =205

option A is correct:

Decreasing the confidence level decreases the sample size needed.

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