geigercounter120 <geigercounter120 <at> yahoo.co.uk> writes: > > Hi all, > > I hope that i've posted this in the correct place. if not, please accept my > apologies (where should this go?) > > I have carried out experimental removal of bivalves at 2 intertidal shores. > Bivalves were removed by raking of surface sediments. I wish compare the > biomass values of for a total of 8 species between the 2 shores > > My 3 treatments are: Undisturbed Controls (Cont), Procedural Controls (Proc) > and Experimetnally Fished (Fished). > > As Fished and Proc have both experienced disturbance, I set the model using > 2 factors as follows: > > Controls Procedural Fished > Raked 0 1 1 > Fished 0 0 1 > > As a newcomer to R (& stats!), I am unsure as to how to proceed. > > i am currently adopting the approach > > model<-glm(biomass~Shore*Raked*Species+Shore*Fished*Species) > > And then run post-hoc adjusted pairwise comparisons between signifcant > terms. >
The best thing would be if you (1) found a local expert to help you with the analysis or (2) sat down and read a book-length treatment of stats in R: check out the 'books' section on www.r-project.org (Dalgaard's and Faraway's books seem particularly appropriate) or the contributed documentation page, *or* read Gotelli and Ellison's _Primer of Statistics for Ecologists_ (not in R, but very clear). Learning R and statistics at the same time with only the built-in R documentation is likely to be very frustrating ... There is also an r-sig-ecology mailing list. Your approach doesn't seem completely crazy (you don't need glm() if your data are normally distributed, lm() will work a little bit better), but I would want to know a lot more about the experimental design: how many data points do you have? Are there experimental blocks in the data? If you really want to treat each species as a separate comparison, it might be more straightforward to use the lmList() command from the nlme package to run a biomass~Shore*(Raked+Fished) comparison for each species ... ______________________________________________ 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.
