Take the 2-minute tour ×
Mathematics Stack Exchange is a question and answer site for people studying math at any level and professionals in related fields. It's 100% free, no registration required.

this is the problem:

we wish to estimate the mean execution time of a program. the program was run 35 times on randomly selected inputs, and the sample mean and the sample standard deviation of the execution times were evaluated as (x bar)=230ms, and S(sample sd)=14ms, respectively. find 95% CI for the true mean execution time u

what and how can you tell this is a non-normal population. i knew it because it is an example under "Large sample CI for non-normal population"

share|improve this question
    
Almost nothing is normal. The distribution of long enough sums (and therefore averages) of independent identically distributed "nice" random variables are well approximated by a normal. –  André Nicolas Dec 10 '12 at 18:21

1 Answer 1

There is not enough information here to tell that it's not normal. The point is that because the sample size is somewhat large, it doesn't matter that it's not normal, because of the central limit theorem. However, the sample is not so large that I wouldn't use Student's t-distribution. You'd have $34$ degrees of freedom.

share|improve this answer

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.