-------- Original Message --------
Subject: Re: Time series analysis on landmarks
Date: Fri, 16 Mar 2012 17:43:38 -0400
From: ppi...@uniroma3.it
To: morphmet@morphometrics.org
You should not use CVA to test differences in shape
between any sort of classes (decades, sex, species,
etc.). Use, instead, Procrustes Coordinates. You can
find detailed discussion on morphmet about this topic.
Moreover, there is in the data a temporal
non-independence that should be removed when
performing MANOVA or regression analysis.
Time is a high anisotropic source of covariation
between observations. Variation partitioning could
deal with this situation. Or gls.
I hope this helps
Best
Paolo
-------- Original Message --------
Subject: Time series analysis on landmarks
Date: Fri, 16 Mar 2012 12:11:28 -0400
From: J.C. van Rijssel
<j.c.van.rijs...@biology.leidenuniv.nl>
To: <morphmet@morphometrics.org>
Dear Colleagues,
Currently, I am working on a large dataset of fishes
where I use
preserved specimens up to 30 years ago. This results
in a nice dataset
where I can check if the body shapes of these fishes
have changed over
the past 30 years (at three year time intervals).
After analysis (CVA),
body shape does change within a decade (concurrent
with ecological
changes in the fishes' environment).
However, in the most recent years, the body shape
seems to return back
to the old shape of my first year (also concurrent
with the ecological
changes).
What I would like to know if there is a way to
(statistically) check
whether the body shape has really returned to its
original form or that
this might be just a coincidence that my first and
last year happen to
have the same shape (no significant differences in the
permutation test
of the CVA)?
I think there should be some sort of time series
analysis which could
solve the issue. Does anyone know of a statistical
program which can do
a time series analysis (or autocorrelation) on
landmarks?
Best regards,
Jacco van Rijssel
PhD-Student Integrative Zoology
Leiden University
The Netherlands
--
Paolo Piras
Center for Evolutionary Ecology
and
Dipartimento di Scienze Geologiche, Università Roma Tre
Largo San Leonardo Murialdo, 1, 00146 Roma
Tel: +390657338000
email: ppi...@uniroma3.it
