[R-sig-eco] guidance required (GLM?)

[Christopher Cesar]

Thanks all for your input.

Originally, I was planning on using a simple model with 1 'treatment' factor with 3 levels (control, procedural control, fished), but was concerned that the 'fished' level had also experienced the 'procedural control' disturbance and so that's when I started delving into this possibly overly-complex approach (bbolker on nabble also pointed out that glm is possibly not the best approach).

I think that breaking the data down to run separate analyses on different shores is a worthy approach and will look into this, possibly using either:
Model1<-lm(biomass~species/(Procedural.Control+Control)) #or
Model2<-lm(biomass~species/Treatment)

Thanks again for all responses

Chris

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Today's Topics:

   1. guidance required (GLM?) 

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Message: 1
Date: Wed, 24 Aug 2011 09:02:45 +0000
From: Christopher Cesar <C.Cesar at apemltd.co.uk>
To: "r-sig-ecology at r-project.org" <r-sig-ecology at r-project.org>
Subject: [R-sig-eco] guidance required (GLM?)
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	<FA4191FA9895EE4E8E4AB3794909AC791D612255 at EXCHANGE.APEM.local>
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Hi all,

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
Fished0		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.

Does this look OK to you guys?

Many, many thanks

Chris






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