----- Forwarded message from andrea cardini <alcard...@gmail.com> -----
Date: Thu, 28 Nov 2013 06:15:05 -0500
From: andrea cardini <alcard...@gmail.com>
Reply-To: andrea cardini <alcard...@gmail.com>
Subject: Re: sampling size
To: morphmet@morphometrics.org
Patrick, there's something about this in my EOLSS
paper (which I think you might already have).
Many more variables than specimensis generally
not great for doing stats (especially
parametric). However, this is not what decides
the number of landmarks. The choice of landmarks
(and therefore their number) should be first
determined by your specific hypothesis and maybe
the type of data. I think this is also discussed
in both Oxnard & O'Higgins, 2009, and
Klingenberg, 2008 (cited by Carmelo in a previous message).
Resampling methods using distances are a
possibility when you have many variables.
Dimensionality reduction can be another option.
However, if a sample is really small and group
differences are not huge, parameters like sample
mean, variance etc. will be poorly estimated
(Cardini & Elton, 2007, Zoomorphol.) and that to
me simply means that one needs more specimens. If
more specimens are not available, one needs to
acknowledge that there might be problems with
those small samples and maybe re-do analyses with
and without them to check the sensitivity of general results.
Cheers
Andrea
At 10:59 28/11/2013, you wrote:
>----- Forwarded message from Patrick Arnold <patrick.arn...@uni-jena.de> -----
>
> Date: Tue, 26 Nov 2013 15:53:26 -0500
> From: Patrick Arnold <patrick.arn...@uni-jena.de>
> Reply-To: Patrick Arnold <patrick.arn...@uni-jena.de>
> Subject: sampling size
> To: morphmet@morphometrics.org
>
>Dear all,
>
>I have a very basic question: how many landmarks are suitable for
>certain sample size. I want to examine 60 landmarks of vertebrae. I
>think my sample is too small. Thus, will I need at least 60 vertebrae
>or at least 120, or ....? I do not find a rule or formula for
>calculating sampling size.
>Thanks in advance.
>
>Patrick Arnold
>
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>----- End forwarded message -----
Dr. Andrea Cardini
Researcher in Animal Biology, Dipartimento di
Scienze Chimiche e Geologiche, Università di
Modena e Reggio Emilia, l.go S. Eufemia 19, 41121 Modena, Italy
Honorary Fellow, Centre for Anatomical and Human
Sciences, University of Hull, Cottingham Road,
Hull, HU6 7RX, UK & University of York, Heslington, York YO10 5DD, UK
Adjunct Associate Professor, Centre for Forensic
Science , The University of Western Australia, 35
Stirling Highway, Crawley WA 6009, Australia
E-mail address: alcard...@gmail.com, andrea.card...@unimore.it
WEBPAGE: http://sites.google.com/site/hymsfme/drandreacardini
Summary of research interests at:
http://www.dscg.unimore.it/site/home/ricerca/aree-di-ricerca/evolution-taxonomy-and-forensics.html
FREE Yellow BOOK on Geometric Morphometrics:
http://www.italian-journal-of-mammalogy.it/issue/view/405
or full volume at:
http://www.italian-journal-of-mammalogy.it/public/journals/3/issue_241_complete_100.pdf
Editorial board for:
Zoomorphology:
http://www.springer.com/life+sciences/animal+sciences/journal/435
Journal of Zoological Systematics and
Evolutionary Research: http://www.wiley.com/bw/journal.asp?ref=0947-5745&site=1
Hystrix, the Italian Journal of
Mammalogy: http://www.italian-journal-of-mammalogy.it/
----- End forwarded message -----
