[R] Comparing multiple distributions

jiho jo.irisson at gmail.com
Mon May 21 19:26:13 CEST 2007

Hello eveybody,

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.


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