-------- Original Message -------- Subject: Re: Relative warp question Date: Wed, 10 Feb 2010 09:25:15 +0100 From: Carmelo Fruciano <[email protected]> To: [email protected] References: <[email protected]> morphmet <[email protected]> ha scritto:
RW1 to 3 appear to describe the apparent shape variance I am interested in (i.e. high spired vs flat and aperture size). Do the relative warps correspond directly to the identical partial warps in the weight matrix (e.g. RW1 scores column corresponds to the first variable column in the weight matrix)?
Not usually.
If so could I take the first variable in the weight matrix (assuming it corresponds to RW1) and perform a T test just for this variable between my dark and light colour groups?
Either you use the weight matrix or the relative warp scores matrix, using only one variable is not usually advisable because shape is a multivariate trait defined by ALL the variables in the weight matrix or the relative warp scores matrices. It often happens that along the first RW axis there is some biologically relevant variation (allometric variation, for example) but throwing away other relative warps corresponds to throwing away all the information that is not expressed by that first axis, information that is often biologically relevant and that in my opinion one shouldn't discard a priori.
I have tried using a MANOVA approach, but because these samples weren’t collected specifically with this analysis in mind I am lacking enough samples in each of my colour groups to get sufficient power, but I think a T test on a per variable basis should be OK in the first instance.
A randomization approach on the multivariate dataset maybe? Probably there is people in the list who is more expert in the topic and they'll chime in to give you suggestions on this. You could look at MorphoJ whose CVA and discriminant modules implement randomization-based tests (in this case I'm assuming that you are worried about power but a CVA is still defined on your dataset, I don't know about the behaviour of MorphoJ in case the operation is not defined). Best Carmelo -- Carmelo Fruciano Dipartimento di Biologia Animale University of Catania Tel. +39 095 7306023 Cell. +39 349 5822831 e-mail [email protected] ---------------------------------------------------------------- Universita' di Catania - A.P.Se.Ma. Servizio di Posta Elettronica -- For now, new message AND replies should be sent to: [email protected] /* Replies will be sent to the list. */ For more information visit http://www.morphometrics.org
