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 44 points with 99 % confidence assuming σ=12.5?

A​ 99% confidence level requires (?) subjects.

A​ 95% confidence level requires (?) subjects.

How does the decrease in confidence affect the sample size​ required?

Answer 1

1)for 99% confidence :

for 99 % CI value of z=	2.576
standard deviation =	12.50
margin of error E =	4
required sample size n=(z/E)2 =	65.0

( please try 66 if above comes wrong due to rounding error)

2)

for 95%  confidence level

for 95 % CI value of z=	1.960
standard deviation =	12.50
margin of error E =	4
required sample size n=(z/E)2 =	38.0

decrease in confidence level decrease the need of  sample size​ required