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?
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.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.
