`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 tostudy its variations relatively to several factors (time of day,species, water column structure etc.). So my data is special inthat, at each sampling site (each observation), I don't have *one*number, I have *several* numbers (abundance of organisms in eachdepth bin, I sample 5 depth bins) which describe a verticaldistribution.Then let say I want to compare speciesA with speciesB, I would endup trying to compare a group of several distributions with anothergroup of several distributions (where a "distribution" is a vectorof 5 numbers: an abundance for each depth bin). Does anyone knowhow 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 andcompare the two mean distributions with a ks.test but thisobviously diminishes the power of the test (I only compare 5*2"observations")- restrict the information at each sampling site to the mean depthweighted by the abundance of the species of interest. This way Ihave one observation per station but I reduce the information tothe mean depths while the actual repartition is important also.I know this is probably not directly R related but I have alreadysearched around for solutions and solicited my local statisticsexpert... to no avail. So I hope that the stats' experts on thislist will help me.Thank you very much in advance.

JiHO --- http://jo.irisson.free.fr/ -- Ce message a été vérifié par MailScanner pour des virus ou des polluriels et rien de suspect n'a été trouvé. CRI UPVD http://www.univ-perp.fr

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