[SciPy-User] MannWhitneyU test critical values

josef.pktd@gmai... josef.pktd@gmai...
Thu Sep 9 06:04:09 CDT 2010


On Thu, Sep 9, 2010 at 5:14 AM, <kossnair@web.de> wrote:

>  Hi there,
> I just choke on a trivial problem (I think):
> I have 13 test data sets and two methods, that return a measure of
> performance. (higher value is better)
> Now I want to use scipy.stats.mannwhitneyu for significance testing.
> However, I did not find a possibility to retrieve a critical value.
> If I am right the method returns a critical value, that has to be compared
> with a tabulated value.
> Can anybody point me towards a way of reading this tabulated value in a
> python script?
> Thank you very much in advance,
> kossnair
>

All statistical tests (except anderson-darling) return p-values, which you
can use to decide whether to reject or not to reject the null hypothesis.
For example, a pvalue below 0.05 means, the null hypothesis can be rejected
with an alpha of 5 % (confidence level 1-alpha).

For the actual critical values, we have to look at the source to see which
distribution for the test-statistic is used. I don't remember what
mannwhitneyu uses, and I don't have time until later to look it up.


Josef




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