Posted by **Megan** on Sunday, May 5, 2013 at 5:51pm.

A doctor wants to estimate the HDL cholesterol of all 20-29 year old females. How many subjects are needed to estimate the HDL cholesterol within 2 points with 99%confidence assuming s=17.8 based on earlier studies? Suppose the doctor would be content with 90% confidence. How does the decrease in cofidence affect the sample size required?

A: A 99% confidence level requires ___ subjects

B: A 90% confidence level requires ___ subjects

- 7 STATS MATHGURU PLEASE HELP -
**MathGuru**, Sunday, May 5, 2013 at 6:07pm
2.58 = 99% confidence interval

1.645 = 90% confidence interval

Use a formula to find sample size.

Here is one:

n = [(z-value * sd)/E]^2

...where n = sample size, z-value = values above for the intervals needed, sd = 17.8, E = .02, ^2 means squared, and * means to multiply.

Plug the values into the formula and finish the calculations. Round your answers to the next highest whole number.

I'll let you take it from here.

- 7 STATS MATHGURU PLEASE HELP -
**hi**, Wednesday, April 6, 2016 at 9:48pm
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 44 points with 99 %99% confidence assuming s equals 11.2s=11.2 based on earlier studies? Suppose the doctor would be content with 90 %90% confidence. How does the decrease in confidence affect the sample size required?

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