Il 03/11/22 15:19, ying yi ha scritto:
Dear all,
I used the “procD.lm” function in the geomorph package to test the
measurement error. I was surprised to find that the within-groups ANOVA
sum of squares I got was greater than the among-groups ANOVA sum of
squares. I wonder if something went wrong. What does it mean for
“procD.lm” function to get an F value <1?
I would be very happy if someone could help me.
Yours,
Sam
Dear Sam,
I saw you attached my review on the topic so I thought I would chime in.
If your within-group sum of squares is larger it can be that you have
large measurement error.
However, I'd like to point out that in this case by "group" one means
"individual" as the usual way of running a Procrustes ANOVA to quantify
measurement error is to use the "individual" as predictor/factor. When
run this way on a dataset with repeated measurements, the
"group"/"individual" sum of squares quantifies the variation among
individuals (e.g., specimens) and the "within group"
("within-individual" or residual) sum of squares quantifies the
variation among repeated measurements of the same individuals.
I'm not saying this is your case, but sometimes I've come across
Procrustes ANOVAs with different designs interpreted as if they were
appropriate to quantify measurement error (for instance, using
"repetition" as a predictor/factor). So I thought I would point that out
to avoid confusion in others.
Best,
Carmelo
--
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Carmelo Fruciano
Italian National Research Council (CNR)
IRBIM Messina
http://www.fruciano.org/
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