[R] t-test problem

Cliff Lunneborg cliff at ms.washington.edu
Wed Sep 22 23:27:31 CEST 2004

Kan Liu wrote:

> 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

If you are unsure about the metric of the attribute being measured, it
would be preferable to use a rank test, the Wilcoxon-Mann-Whitney,
rather than the parametric t-test.

Cliff Lunneborg, Professor Emeritus, Statistics &
Psychology, University of Washington, Seattle
cliff at ms.washington.edu

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