Posted by
Maguin, Eugene on
Aug 19, 2011; 12:55pm
URL: http://spssx-discussion.165.s1.nabble.com/fixed-effect-with-ancova-tp4713723p4715776.html
Ro,
I don't think you have an ancova design. Why do you think you do?
I disagree with your model statement. Your design statement implies that you
have the weights of the individual fish; so, 15*8*3=360 data points. You
don't. You have the weights of a tank of fish; so, 8*3=24 data points. I say
you have a one factor anaova in which the factor is diet and you have three
data points (tank weights) per level of diet.
Gene Maguin
-----Original Message-----
From: SPSSX(r) Discussion [mailto:
[hidden email]] On Behalf Of ro
Sent: Thursday, August 18, 2011 6:57 PM
To:
[hidden email]
Subject: fixed effect with ancova
Hi all,
I need calculate fixed effect with ancova analysis (spss or genstat).
My experiment was on fishes weight with differents diets (8): 15 fishes in
each tank (each diet in triplicated, 3 tanks for each diet, total tanks:24).
I need calculate p value for fixed effect: tanks and diets wit ancova
analysis. the correct or desired model is
weight= Intercept + Diet_Effect + tank_effect+ epsilon
when i do this analysis with just one effect (tank or diet separatedly) i
found significants differences (this is the expected result), but when i do
the analysis with both effect in the same ancova analysis (the correct
method) i dont found significant diferences in diet...
I did read that the correct methods for this kind of problem coul be with
blocks or nested method or just interaction tanks*diet, i hope capture
variance produced by tanks
my spredsheet looks like
diet tank weight
1 1
1 2
1 3
2 4
2 5
2 6
3 7
3 8
3 9
...
Any recomendation is valuable.
--
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