The Student Room Group

Mann-Whitney test critical values table

I'm doing some stats for a piece of Geography work atm (*shudder*) and i don't want to walk all the way down to the library to try to find a book with a table of critical values for the Mann Whitney U test. I'm sure there must be one on the 'net somewhere, but does anyone know where?

Of course i've tried googling, but all i can come up with is several tables which only go up to n=20 (i need n=34), and some kind of automatic calculator which is not what i want at all.

Thanks for any links you can find
Reply 1
The tables don't go above 20 because when n1 and n2 are large you can use a normal approximation. See http://www.cquest.utoronto.ca/geog/ggr270y/tables/Mann-Whitney_U_Table.html. You need to calculate Z and compare it to the critical values of the N(0, 1) distribution. If you post your values of n1, n2 and u, I'll do the sums for you.
Have posted a reply over the Geog forum where you posted this topic also, but anyway:

Mann-Whitney U for n1=n2=34

5% u*=418
1% u*=369


(Neave's Statistical Tables).
Reply 3
Thanks.
Reply 4
Aha. I just realised where i screwed up....my n isn't 34, it's 17. So i can just look it up in the many tables out there that go up to 20. Stupid stats...shouldn't be in geog at all :frown:

Thanks anyway though.
Tom
Aha. I just realised where i screwed up....my n isn't 34, it's 17. So i can just look it up in the many tables out there that go up to 20. Stupid stats...shouldn't be in geog at all :frown:

Thanks anyway though.



You won't have been the first to not count the sample sizes before combining the results - trust me, too easy a mistake to make.

At least you spotted it now though !
I am also in a similar situation where my n1 and n2 values are both 30. Would anyone be able to assist in helping me do the calculations if I provide the necessary data?
thanks a lot
Susan
I also have another problem that I need to solve regarding the Mann-Whitney test:

I can't find any information about minus and zero values and how to calculate them. Can anyone help?
thanks
Susan
Reply 8
ok just spent a while doing this

you shouldn't be getting minus or negative values but this will do the test for you:
http://faculty.vassar.edu/lowry/utest.html

and that will give you a z-value and its associated probability (ie whether to reject your null)

also the critical values up to 30 are here, so you could just use your u value (rather than z value which i realise may be confusing you, but I don't have time to explain right now!) which the above page will calculate:
http://www.social-science.co.uk/stats_CV.php

hope this helps