15. A doctor wants to estimate the mean HDL cholesterol of all 20- to 29-year-ol

Question

15. 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 4 points with 99% confidence assuming s= 15.3 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 A 95% confidence level requires How does the decrease in confidence affect the sample size required? subjects. (Round up to the nearest subject.) subjects. (Round up to the nearest subject.) A. The sample size is the same for all levels of confidence. 0 B. Decreasing the confidence level decreases the sample size needed. ° C. Decreasing the confidence level increases the sample size needed.

Explanation / Answer

Sample size for 99% confidence level is

n = z2 * S2 / E2

= 2.57582 * 15.32 / 42

= 97.07

Sample size = 98 (Rounded up to nearest integer)

Sample size for 95% level.

n = z2 * S2 / E2

= 1.962 * 15.32 / 42

= 56.21

Sample size = 57 (Rounded up to nearest integer)

So, Decreasing confidence level decreases the sample size required.

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