Question

Determining the sample size Find out the sample size needed to determine the average monthly income per student customer for a university cafeteria.

Answer 1

Explanation:

Necessary Sample Size = (Z-score)² * StdDev*(1-StdDev) / (margin of error)²

For example, given a 95% confidence level, 0.5 standard deviation, and a margin of error (confidence interval) of +/- 5%. Necessary Sample Size =

((1.96)² x 0.5(0.5)) / (0.05)²

(3.8416 x 0.25) / .0025

0.9604 / 0.0025

384.16

So in order to get 95% confidence level, with confidence interval of +/- 5%, and standard deviation of 0.5, I have to survey 385 samples.

As I usually calculate the average value on 100 samples. So what is the confidence level I can get?

Is anyone who has experience on this can share something?

Thanks a lot!