[SciPy-user] help with scipy.stats.mannwhitneyu
Thu Feb 5 12:16:22 CST 2009
On Thu, Feb 5, 2009 at 1:03 PM, Sturla Molden <email@example.com> wrote:
> On 2/5/2009 6:46 PM, firstname.lastname@example.org wrote:
>> so whether bigU or smallU is used in the calculation of z doesn't
>> matter, I have no idea why in this specific implementation both are
>> calculated if smallU would be enough.
> By the way, there is a fucntion scipy.stats.ranksums that does a
> Wilcoxon rank-sum test. It seems to be using a large-sample
> approximation, and has no correction for tied ranks.
Also, in the explanation for kruskal it says it's an extension of
Mann-Whitney-U to more than 2 groups
for 2 groups (no ties):
>>> stats.kruskal(rvs1,rvs2) - stats.mannwhitneyu(rvs1,rvs2)*2
>>> stats.kruskal(rvs1,rvs2) - stats.ranksums(rvs1,rvs2)
>>> stats.ranksums(rvs1,rvs2) - stats.mannwhitneyu(rvs1,rvs2)*2
It looks like there are some redundancies or small variations in these
tests. A systematic list of all tests would be pretty useful.
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