A doctor wants to estimate the mean HDL cholesterol of all 2

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=13.1 based on earlier studies? Suppose the doctor would be content with 90% confidence. How does the decrease in confidence affect the sample size?

A 99% confidence level requires ___ subjects (round up to the nearest subjet)

Solution

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=13.1 based on earlier studies? Suppose the doctor would be content with 90% confidence. How does the decrease in confidence affect the sample size?

For 99%, z=2.576

d=4

sd=13.1

Sample size = (z²*s²)/d²

= (2.576²*13.1²)/4²

=71.17

The sample size required= 72

A 99% confidence level requires 72 subjects (round up to the nearest subjet)

Suppose the doctor would be content with 90% confidence.

The decrease in confidence level decreases the sample size.