Dear Jens,
you might want to consider working with multivariate analyses (i.e.
using all PCs and not a single one) and, as it has been suggested,
using (multivariate) linear models rather than dividing scores by your
size measure.
Best,
Carmelo
--
Carmelo Fruciano
Honorary Fellow - University of Catania - Catania, Italy
e-mail [email protected]
http://www.fruciano.it/research/
Jens De meyer <[email protected]> ha scritto:
Dear,
I have a question about EFDs, and was wondering if you could help
me? I have performed a PCA on standardized EFDs (standardized for
first harmonic, using SHAPE-software). The EFDs represented head
shapes of eels which were given different diets (we compared three
different diets). The results of the PCA indicated that PC1 was
related to variation in head width, with high PC-scores being
related to broader heads and vice versa. Next, we performed a linear
regression on these PC-scores and log(length) of the three different
diets and observed a size-effect in all three diets.
Because of this, I wanted to divide the PC-scores by the total
length of the studied eels. Then, we would perform an ANOVA on these
length-corrected PC-scores between the different diets, as this
would allow us to find out whether the mean head width of a certain
diet is significantly broader than another diet.
Therefore, my question to you is: Am I acutally allowed to divide
these PC-scores by total length?
Many thanks in advance!
Kind regards,
Jens De Meyer
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--
Carmelo Fruciano
Honorary Fellow - University of Catania - Catania, Italy
e-mail [email protected]
http://www.fruciano.it/research/
--
MORPHMET may be accessed via its webpage at http://www.morphometrics.org
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