Question

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 3 points with 99% confidence assuming s= 18.2 based on earlier studies? Supposed the doctor will be content with 90% confidence. How does the decrease in confidence affect the sample size required?
A 99% confidence level requires_ subjects?

Answer 1

Given that, standard deviation ( s )= 18.2

margin of error ( E ) = 3

we want to find the sample size ( n ),

1) a 99% confidence level has critical value is,

Then sample size is,

A 99% confidence level requires 244 subjects.

2) a 90% confidence level has critical value is,

then the sample size is,

A 90% confidence level requires 100 subjects.

3) As we decreases the confidence level the sample size also decreases.

Therefore, decreasing the confidence level decreases the sample size needed.