Hi Liu,
before applying a t-test (or any test) you should first check if the assumptions of the test are supported by your data, i.e., in a t-test x and y must be normally distributed.
I hope it helps.
Best, Dimitris
---- Dimitris Rizopoulos Ph.D. Student Biostatistical Centre School of Public Health Catholic University of Leuven
Address: Kapucijnenvoer 35, Leuven, Belgium Tel: +32/16/396887 Fax: +32/16/337015 Web: http://www.med.kuleuven.ac.be/biostat/ http://www.student.kuleuven.ac.be/~m0390867/dimitris.htm
----- Original Message ----- From: "kan Liu" <[EMAIL PROTECTED]>
To: <[EMAIL PROTECTED]>
Sent: Wednesday, September 22, 2004 9:52 AM
Subject: [R] t test problem?
Hello,
I got two sets of data
x=(124738, 128233, 85901, 33806, ...)
y=(25292, 21877, 45498, 63973, ....)
When I did a t test, I got two tail p-value = 0.117, which is not significantly different.
If I changed x, y to log scale, and re-do the t test, I got two tail p-value = 0.042, which is significantly different.
Now I got confused which one is correct. Any help would be very appreciated.
Thanks, Liu
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