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 2 points with 99 % confidence assuming s equals 13.7 based on earlier​ studies? Suppose the doctor would be content with 90 % confidence. How does the decrease in confidence affect the sample size​ required?

Answer 1

Answer:

Sample size = ( Z/2 * S / E)²

Where,

Z/2 is critical value at given significance level,

S is standard deviation

E is margin of error.

a)

For 99% confidence level,

Sample size = (2.5758* 13.7 / 2)²

= 311.31

Sample size = 312 (Rounded up to nearest integer)

For 90% confidence level,

Sample size = (1.645* 14.3 / 2)²

= 138.33

Sample size = 139 (Rounded up to nearest integer)

So, Sample size required decreases if we decrease in confidence level.

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