That said, > wilcox_test(x ~ factor(y), distribution = "exact")
or the same with oneway_test, i.e would be ok? 2013/1/27 Achim Zeileis <achim.zeil...@uibk.ac.at> > On Sun, 27 Jan 2013, Kay Cichini wrote: > > Thanks for the reply! >> >> Still, aren't there issues with 2-sample test vs y and excess zeroes >> (->many ties), like for Mann-Whitney-U tests? >> > > If you use the (approximate) exact distribution, that is no problem. > > The problem with the Wilcoxon/Mann-Whitney test and ties is only that the > simple recursion formula for computing the exact distribution only works > without ties. Thus, it's not the exact distribution that is wrong but only > the standard algorithm for evaluating it. > > Best, > Z > > Kind regards, >> Kay >> >> >> 2013/1/26 Achim Zeileis <achim.zeil...@uibk.ac.at> >> >> On Fri, 25 Jan 2013, Kay Cichini wrote: >>> >>> Hello, >>> >>>> >>>> I'm searching for a test that applies to a dataset (N=36) with a >>>> continuous zero-inflated dependent variable >>>> >>>> >>> In a regression setup, one can use a regression model with a response >>> censored at zero. survreg() in survival fits such models, tobit() in AER >>> is >>> a convenience interface for this special case. >>> >>> If the effects of a regressor can be different for the probability of a >>> zero and the mean of the non-zero observations, then a two-part model can >>> be used. E.g. a probit fit (via glm) plus a truncated regression (via >>> truncreg in the package of the same name). >>> >>> However: >>> >>> >>> and only one nominal grouping variable with 2 levels (balanced). >>> >>>> >>>> >>> In that case I would probably use no regression model but two-sample >>> permutation tests, e.g. via the "coin" package. >>> >>> >>> In fact there are 4 response variables of this kind which I plan to test >>> >>>> seperately - the amount of zeroes ranges from 75 to 97%.. >>>> >>>> >>> That means you have between one (!) and nine non-zero observations. In >>> the >>> former case, it will be hard to model anything. And even in the latter >>> case >>> it will be hard to investigate the probability of zero and the mean of >>> the >>> non-zero observations separately. >>> >>> I would start out with a simple two-way table of (y > 0) vs group and >>> conduct Fisher's exact test. >>> >>> And then you might try also your favorite two sample test of y vs group, >>> preferably using the approximate exact distribution. >>> >>> Hope that helps, >>> Z >>> >>> I searched the web and found several modelling approaches but have the >>> >>>> feeling that they are overly complex for my very simple dataset. >>>> >>>> Thanks in advance for any help! >>>> Kay >>>> >>>> -- >>>> >>>> Kay Cichini, MSc Biol >>>> >>>> Grubenweg 22, 6071 Aldrans >>>> >>>> Tel.: 0650 9359101 >>>> >>>> E-Mail: kay.cich...@gmail.com >>>> >>>> Web: www.theBioBucket.blogspot.co.****at<http://www.theBioBucket.** >>>> blogspot.co.at <http://www.theBioBucket.blogspot.co.at>> >>>> <http://www.thebiobucket.**blo**gspot.co.at/ <http://blogspot.co.at/>< >>>> http://www.**thebiobucket.blogspot.co.at/<http://www.thebiobucket.blogspot.co.at/> >>>> > >>>> >>>>> <http://www.**theBioBucket.**blogspot.co.at<http://theBioBucket.blogspot.co.at> >>>>> <http://www.**theBioBucket.blogspot.co.at<http://www.theBioBucket.blogspot.co.at> >>>>> > >>>>> >>>>> -- >>>> >>>> [[alternative HTML version deleted]] >>>> >>>> ______________________________****________________ >>>> R-help@r-project.org mailing list >>>> https://stat.ethz.ch/mailman/****listinfo/r-help<https://stat.ethz.ch/mailman/**listinfo/r-help> >>>> <https://stat.**ethz.ch/mailman/listinfo/r-**help<https://stat.ethz.ch/mailman/listinfo/r-help> >>>> > >>>> PLEASE do read the posting guide http://www.R-project.org/** >>>> posting-guide.html >>>> <http://www.R-project.org/**posting-guide.html<http://www.R-project.org/posting-guide.html> >>>> > >>>> >>>> and provide commented, minimal, self-contained, reproducible code. >>>> >>>> >>>> >> >> -- >> >> Kay Cichini, MSc Biol >> >> Grubenweg 22, 6071 Aldrans >> >> Tel.: 0650 9359101 >> >> E-Mail: kay.cich...@gmail.com >> >> Web: >> www.theBioBucket.blogspot.co.**at<http://www.theBioBucket.blogspot.co.at> >> <http://www.thebiobucket.**blogspot.co.at/<http://www.thebiobucket.blogspot.co.at/> >> ><http://www.**theBioBucket.blogspot.co.at<http://www.theBioBucket.blogspot.co.at> >> > >> -- >> >> [[alternative HTML version deleted]] >> >> ______________________________**________________ >> R-help@r-project.org mailing list >> https://stat.ethz.ch/mailman/**listinfo/r-help<https://stat.ethz.ch/mailman/listinfo/r-help> >> PLEASE do read the posting guide http://www.R-project.org/** >> posting-guide.html <http://www.R-project.org/posting-guide.html> >> and provide commented, minimal, self-contained, reproducible code. >> >> -- Kay Cichini, MSc Biol Grubenweg 22, 6071 Aldrans Tel.: 0650 9359101 E-Mail: kay.cich...@gmail.com Web: www.theBioBucket.blogspot.co.at<http://www.thebiobucket.blogspot.co.at/><http://www.theBioBucket.blogspot.co.at> -- [[alternative HTML version deleted]] ______________________________________________ R-help@r-project.org mailing list 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.
