[R] Glitch in Kruskal-Wallis test?

[David L Carlson]

You may need to spend some more time with the statistician who needs to see your data. It is not clear if you have a two sample test or a paired sample test. Kruskall-Wallis expects data for each observation, not grouped data. Without the observations, the test cannot compute the sample size and the degrees of freedom. You have run kruskal.test separately on each sample. The kruskal.test is designed for comparing two or more samples. 

----------------------------------------
David L Carlson
Department of Anthropology
Texas A&M University
College Station, TX 77843-4352

-----Original Message-----
From: R-help <r-help-bounces using r-project.org> On Behalf Of Jenny Liu
Sent: Saturday, December 22, 2018 7:10 AM
To: Michael Dewey <lists using dewey.myzen.co.uk>
Cc: r-help using r-project.org
Subject: Re: [R] Glitch in Kruskal-Wallis test?

Hi Michael,

Thank you for your reply! I'm testing the difference in proportions. Temp
is temperature, and Prop is the proportion of insect pupae that survived at
that temperature. I was told by a statistician that the K-W was appropriate
for testing proportions, but perhaps you know of an alternative? I have
already tested for heteroscedasticity using the Breusch-Pagan test.

Thanks again,
Jenny



On Dec 22, 2018 7:38 AM, "Michael Dewey" <lists using dewey.myzen.co.uk> wrote:

Dear Jenny

What exactly do you think you are testing here? You are telling K-W you
have seven groups each with a single value which is not the usual
situation for K-W.

Michael


On 22/12/2018 04:58, Jenny Liu wrote:
> Hi everyone,
> I have been running a K-W test with the attached data, PupMort1. My code:
> kruskal.test(Prop~Temp,data=PupMort1)
> However, I found that I get the exact same result when I change the
x-values, as
> in the attached data PupMort2.
> Test run with PupMort1Kruskal-Wallis rank sum testdata:  Prop by Temp

> Kruskal-Wallis chi-squared = 6, df = 6, p-value = 0.4232
> Test run with PupMort2Kruskal-Wallis rank sum testdata:  Prop by Temp

> Kruskal-Wallis chi-squared = 6, df = 6, p-value = 0.4232
> Does anybody know why this is happening?
> Thank you!
> Jenny
>
>
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-- 
Michael
http://www.dewey.myzen.co.uk/home.html

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