[R] R (&stats) newcomer.... help!

[Ben Bolker]

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 ...