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=19.2 based on earlier studies? Suppose the doctor would be content with 90% confidence. How does the decrease in confidence affect the sample size required?

. A 99% confidence level requires____subjects.

Level of Confidence, (1

)

100%

Area in Each Tail,

2

Critical Value,

z/2

90%

0.05

1.645

95%

0.025

1.96

99%

0.005

2.575