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 at 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 thex-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 at r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guidehttp://www.R-project.org/posting-guide.html> and provide commented, minimal, self-contained, reproducible code. >-- Michael http://www.dewey.myzen.co.uk/home.html [[alternative HTML version deleted]]
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 at r-project.org> On Behalf Of Jenny Liu Sent: Saturday, December 22, 2018 7:10 AM To: Michael Dewey <lists at dewey.myzen.co.uk> Cc: r-help at 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 at 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 thex-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 at r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guidehttp://www.R-project.org/posting-guide.html> and provide commented, minimal, self-contained, reproducible code. >-- Michael http://www.dewey.myzen.co.uk/home.html [[alternative HTML version deleted]] ______________________________________________ R-help at 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.
... 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 at 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 at r-project.org> On Behalf Of Jenny Liu > Sent: Saturday, December 22, 2018 7:10 AM > To: Michael Dewey <lists at dewey.myzen.co.uk> > Cc: r-help at 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 at 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 at 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. > > > > -- > Michael > http://www.dewey.myzen.co.uk/home.html > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at 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. > > ______________________________________________ > R-help at 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. >[[alternative HTML version deleted]]