Question

A doctor wants to estimate the HDL cholesterol of all​ 20- to​ 29-year-old females. How many subjects are needed to estimate the HDL cholesterol within 4 points with 99 % confidence assuming sigma equals 11.4 question mark 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 whole number as​ needed.) A 95 % confidence level requires nothing subjects. ​(Round up to the nearest whole number as​ needed.) How does the decrease in confidence affect the sample size​ required? A. The sample size is the same for all levels of confidence. B. The lower the confidence level the larger the sample size. C. The lower the confidence level the smaller the sample size.

Answer 1

Critical value of z for 99% confidence interval , , is . The margin of error is E= 4. And so required sample size will be

So required sample size for 99% confidence interval is 45.

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Critical value of z for 95% confidence interval , , is . The margin of error is E= 4. And so required sample size will be

So required sample size for 95% confidence interval is 32.

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Correct option is:

C. The lower the confidence level the smaller the sample size.