I am to decide whether there is a statistical difference between two
groups concerning variable X.
Variable X distribution is not normal, it is right-skewed.
Log-transformed X distribution is normal (it's histogram looks normal,
it mathces Kolmogorov-S. and Lillefors statistics)
I compared results from Mann-Whitney test and t-Student test on
log-transformed data.
Here are the results:
Mann-Whitney U test
raw data
-------------------
n mean SD median min-max
X1 30 1.43 0.7 1.21 0.26-4.02
X2 6 1.00 0.2 1.0 0.78-1.28
p=0.014
t-Student test
log-transformed data
------------------------
n mean SD
X1 30 0.26 0.46
X2 6 -0.11 0.17
p=0.17
The conclusions seem to be diverse. Nonparametric test shows that the
difference between groups is significant, and parametric test on
log-transformed data shows that there is no such difference.
I am not skilled enough (yet) to interpret these results. Which result
should i trust?
.
.
=================================================================
Instructions for joining and leaving this list, remarks about the
problem of INAPPROPRIATE MESSAGES, and archives are available at:
. http://jse.stat.ncsu.edu/ .
=================================================================
