×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

about standard deviation in ttest

about standard deviation in ttest

about standard deviation in ttest

(OP)
Hi,

I have a question about the calculation of standard deviation in ttest. From matlab help, ttest uses the sample
standard deviation which is the total squared error divided by (n-1).

From wiki, it says the grand standard deviation of sample is used (divided by n or n-1?). Are the two the same?

Thanks,

Mapi

RE: about standard deviation in ttest

Well, for a large population, it doesn't matter much, does it?

For small populations, the correct answer is n-1, since that's the degrees of freedom in the data.

But, basically, if you have more than 10 samples, the difference is pretty small compared to all the potential error sources, including the standard deviation of the mean.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

RE: about standard deviation in ttest

(OP)
Thanks.

Just because my sample size is less than 5, I have to be very careful about it.

mapi

RE: about standard deviation in ttest

for 5, I would go with n-1, but the variance of the mean will be commensurate, so the standard deviation is going to be pretty rough, no matter what.

TTFN

FAQ731-376: Eng-Tips.com Forum Policies

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources