[R] Glitch in Kruskal-Wallis test?

[Bert Gunter]

... Moreover, you should not analyze proportions in this way, which treats
.5 = 2/4 or .5 = 2000/4000 identically. As David said, you need to work
with a statistician.

Bert Gunter

"The trouble with having an open mind is that people keep coming along and
sticking things into it."
-- Opus (aka Berkeley Breathed in his "Bloom County" comic strip )


On Sat, Dec 22, 2018 at 7:32 AM David L Carlson <dcarlson using tamu.edu> wrote:

> 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
> >
> >
> > ______________________________________________
> > R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
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> > and provide commented, minimal, self-contained, reproducible code.
> >
>
> --
> Michael
> http://www.dewey.myzen.co.uk/home.html
>
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>
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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