Adoctor 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 = 11.1 based on earlier studies? suppose the doctor would be content with 95% confidence. how does the decrease in confidence affect the sample size?

99% requires subjects

95% requires subjects

how does the decrease in confidence affect the sample size?

99% confidence requires 243 subjects

95% confidence requires 118 subjects

The decrease in confidence makes the sample size smaller.

Step-by-step explanation:

The sample size n in Simple Random Sampling is given by

where  

z = 2.807 is the critical value for a 99% confidence level (*)

s = 11.1 is the estimated population standard deviation

e = 2 points is the margin of error

so  

(*)This is a point z such that the area under the Normal curve N(0,1) outside the interval [-z, z] equals 1% = 0.001

It can be obtained in Excel with

=NORMINV(1-0.0025,0,1)

and in OpenOffice Calc with

=NORMINV(1-0.0025;0;1)

A 95% confidence level would only change the value of z, which now would be 1.96, and the sample size changes to

The decrease in confidence makes the sample size smaller.

the simplified form is

step-by-step explanation:

we want to simplify the expression,

let us change the middle bar to a normal division sign to obtain,

we multiply the first fraction by the reciprocal of the second fraction to obtain,

we factor to obtain,

we cancel the common factors to get,

we simplify to get,

the correct answer is b