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st: R: Re: choice of ANOVA for an ecological experiment
From
"Carlo Lazzaro" <[email protected]>
To
<[email protected]>
Subject
st: R: Re: choice of ANOVA for an ecological experiment
Date
Mon, 31 Jan 2011 19:17:41 +0100
Dear Jacob,
I am not an expert in this field. For more details on split plot (and
alternative designs), a good reference for your research is Doncaster CP,
Davey AJH. Analysis of Variance and Covariance. How to choose and construct
models for the life sciences. Cambridge: 2007. This textbook devotes an
entire 5th chapter to split-plot designs (pages 141-178) and a worked
example of split-plot model is detailed at pages 51-57.
Sorry I cannot be more helpful.
Kind Regards,
Carlo
-----Messaggio originale-----
Da: [email protected]
[mailto:[email protected]] Per conto di Jacob Felson
Inviato: lunedì 31 gennaio 2011 18.28
A: [email protected]
Oggetto: st: Re: choice of ANOVA for an ecological experiment
Carlo,
Good question. I've also done a MANOVA, yes. For the MANOVA as well,
I'm wondering about the appropriate way to analyze the data -- split
plot or something else.
Jacob Felson
On Sun, Jan 30, 2011 at 3:00 PM, Jacob Felson <[email protected]> wrote:
> Hello,
>
> I am wondering whether anyone might be able to advise me about the
> best choice of ANOVA to analyze the results of an ecological
> experiment. In each of eight ponds, a certain number of various
> species were put into enclosures that were randomly assigned to a set
> of four predator conditions. The four randomly assigned predator
> conditions were: no predators, 8 predators, 16 predators, and 24
> predators. Each predator condition was assigned to 3 replicates. So
> the total number of enclosures was: 8 ponds x 4 predator conditions x
> 3 replicates = 96. The outcome variables include the number of
> individuals remaining, the weight of the individuals remaining, and
> the size of the individuals remaining.
>
> This experiment appears to follow a split-plot design. Is this
> correct? That is, the error of the pond effect is distinct from the
> error of the predator condition effect. The sum of squared error for
> the pond would be equal to the sum of squares for the predator
> condition. The sum of squared error for the predator condition would
> be equal to the residual sum of squares.
>
> The predator condition variable is called density, and the outcome
> variable is number of survivors. If all of this is accurate, then I'm
> guessing that a simple model might be:
>
> anova survivors pond / density | pond /
>
>
> Is this correct? One further issue is that the ponds are fixed, not
> random. Unlike the textbook split-plot design, a whole-plot has not
> been randomly assigned to ponds. Instead, there are simply 8 ponds,
> within each of which individuals were collected and placed in
> enclosures with varying predator conditions.
>
>
> I would very much appreciate help on this issue!
>
>
> Sincerely,
> Jacob Felson
>
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