Your data is "compositional data". The R package "compositions" might be useful. You might also want to consult the book by J. Aitchison: statistical analysis of compositional data.

Ravi. ---------------------------------------------------------------------------- ------- Ravi Varadhan, Ph.D. Assistant Professor, The Center on Aging and Health Division of Geriatric Medicine and Gerontology Johns Hopkins University Ph: (410) 502-2619 Fax: (410) 614-9625 Email: [EMAIL PROTECTED] Webpage: http://www.jhsph.edu/agingandhealth/People/Faculty/Varadhan.html ---------------------------------------------------------------------------- -------- -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of jiho Sent: Thursday, May 31, 2007 11:37 AM To: R-help Subject: Re: [R] Comparing multiple distributions Nobody answered my first request. I am sorry if I did not explain my problem clearly. English is not my native language and statistical english is even more difficult. I'll try to summarize my issue in more appropriate statistical terms: Each of my observations is not a single number but a vector of 5 proportions (which add up to 1 for each observation). I want to compare the "shape" of those vectors between two treatments (i.e. how the quantities are distributed between the 5 values in treatment A with respect to treatment B). I was pointed to Hotelling T-squared. Does it seem appropriate? Are there other possibilities (I read many discussions about hotelling vs. manova but I could not see how any of those related to my particular case)? Thank you very much in advance for your insights. See below for my earlier, more detailed, e-mail. On 2007-May-21 , at 19:26 , jiho wrote: > I am studying the vertical distribution of plankton and want to > study its variations relatively to several factors (time of day, > species, water column structure etc.). So my data is special in > that, at each sampling site (each observation), I don't have *one* > number, I have *several* numbers (abundance of organisms in each > depth bin, I sample 5 depth bins) which describe a vertical > distribution. > > Then let say I want to compare speciesA with speciesB, I would end > up trying to compare a group of several distributions with another > group of several distributions (where a "distribution" is a vector > of 5 numbers: an abundance for each depth bin). Does anyone know > how I could do this (with R obviously ;) )? > > Currently I kind of get around the problem and: > - compute mean abundance per depth bin within each group and > compare the two mean distributions with a ks.test but this > obviously diminishes the power of the test (I only compare 5*2 > "observations") > - restrict the information at each sampling site to the mean depth > weighted by the abundance of the species of interest. This way I > have one observation per station but I reduce the information to > the mean depths while the actual repartition is important also. > > I know this is probably not directly R related but I have already > searched around for solutions and solicited my local statistics > expert... to no avail. So I hope that the stats' experts on this > list will help me. > > Thank you very much in advance. JiHO --- http://jo.irisson.free.fr/ -- Ce message a iti virifii par MailScanner pour des virus ou des polluriels et rien de suspect n'a iti trouvi. CRI UPVD http://www.univ-perp.fr ______________________________________________ R-help@stat.math.ethz.ch 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.