Jump to content

  • Log in with Facebook Log in with Twitter Log in with Windows Live Log In with Google      Sign In   
  • Create Account

Submit your paper to J Biol Methods today!
Photo
- - - - -

Method of calculating p value for Pearson's correlation coefficient


  • Please log in to reply
5 replies to this topic

#1 Curtis

Curtis

    Metaller Scientist

  • Global Moderators
  • PipPipPipPipPipPipPipPipPipPip
  • 1,112 posts
59
Excellent

Posted 28 April 2013 - 09:35 PM

I'm not very professional in calculating Pearson's correlation coefficient (r), and I see people use the following formula to calculate the p value for r:

p=r/Sqrt(r^2)/(N—2)

where N is the number of variants.

why don't they just use student's t test? I usually use Excel and chose TTEST function for this matter. It's so easy.

#2 bob1

bob1

    Thelymitra pulchella

  • Global Moderators
  • PipPipPipPipPipPipPipPipPipPip
  • 5,784 posts
406
Excellent

Posted 29 April 2013 - 02:22 PM

Pearson's is used for determining if there is a correlation between variables, a t-test measures the difference between two populations, so they look at different things.

#3 DRT

DRT

    Veteran

  • Active Members
  • PipPipPipPipPipPipPipPipPipPip
  • 161 posts
7
Neutral

Posted 29 April 2013 - 03:37 PM

The formula you have given looks like it should be t=r/Sqrt((1-r^2)/(N—2)) the t statistic for testing if the correlation coefficient is significant, it can then be converted to a p value using the T.DIST function in Excel.

#4 Curtis

Curtis

    Metaller Scientist

  • Global Moderators
  • PipPipPipPipPipPipPipPipPipPip
  • 1,112 posts
59
Excellent

Posted 29 April 2013 - 09:21 PM

Pearson's is used for determining if there is a correlation between variables, a t-test measures the difference between two populations, so they look at different things.


I always use TTEST function and I have no problem. But the above equation gives me different p value which is not similar to the TTEST value. I am still not sure why people use this equation to calculate the p value of those variables. I hope you understand what I' trying to say. I know r is correlation coefficient. by why can't they just use the same TTEST, instead of this equation. it shouldn't be used?

#5 Curtis

Curtis

    Metaller Scientist

  • Global Moderators
  • PipPipPipPipPipPipPipPipPipPip
  • 1,112 posts
59
Excellent

Posted 29 April 2013 - 09:35 PM

The formula you have given looks like it should be t=r/Sqrt((1-r^2)/(N—2)) the t statistic for testing if the correlation coefficient is significant, it can then be converted to a p value using the T.DIST function in Excel.


I checked TDIST. don't know how to fill those gaps.

#6 DRT

DRT

    Veteran

  • Active Members
  • PipPipPipPipPipPipPipPipPipPip
  • 161 posts
7
Neutral

Posted 30 April 2013 - 01:01 PM


The formula you have given looks like it should be t=r/Sqrt((1-r^2)/(N—2)) the t statistic for testing if the correlation coefficient is significant, it can then be converted to a p value using the T.DIST function in Excel.


I checked TDIST. don't know how to fill those gaps.


I found this link with the instructions for getting the obtaining a p value from the correlation coefficient.
http://www.ehow.com/...excel-2007.html

You may also like to install the ‘data analysis’ add-in for excel (under File-Options-Add-Ins) but make sure you come to grips with the different sorts of t-tests first Posted Image Posted Image




Home - About - Terms of Service - Privacy - Contact Us

©1999-2013 Protocol Online, All rights reserved.