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st: Re: choice of ANOVA for an ecological experiment


From   Jacob Felson <felsonj@gmail.com>
To   statalist@hsphsun2.harvard.edu
Subject   st: Re: choice of ANOVA for an ecological experiment
Date   Mon, 31 Jan 2011 12:27:44 -0500

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 <felsonj@gmail.com> 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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