[SciPy-user] help with scipy.stats.mannwhitneyu
Thu Feb 5 08:56:08 CST 2009
Wavy Davy wrote:
> Hi all
> I am using the mannwhitneyu in the stats module, and I was looking the
> code and I see this notice in the docstring.
> "Use only when the n in each condition is < 20 and you have 2
> independent samples of ranks. "
> Am I reading it correctly that this test should only be used with
> sample sizes less than 20?
> I am not a statistican, more a python coder. I have been pointed and
> this test as a more robust version of the t-test, so forgive my
> Any help would be much appreciated.
I think the docstring is referring to the distribution of the actual
U-test. So for small samples typically the pvalue is directly computed
from the sampling distribution. However, Scipy is using the normal
approximation is which is not meant to be that great.
More information about the SciPy-user