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

Question

A doctor wants to estimate the mean HDL cholesterol of ail 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 = 17.3 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.) A 95% confidence level requires subjects. (Round up to the nearest subject.) How does the decrease in confidence affect the sample size required? A. Decreasing the confidence level decreases the sample size needed. B. The sample size is the same for all levels of confidence. C. Decreasing the confidence level increases the sample size needed.

Explanation / Answer

99% confidence level:

n = (zc * SD)^2 / E^2

For 99% the critical z is given by 2.58

n = (2.58*17.3)^2/2^2

   = 498

Answer: 498

For 95% the critical z is given by 1.96

n = (1.96*17.3)^2/2^2

   = 287

Answer: 287

Answer: Decreases the confidence level decreases the sample size needed.

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