----- Forwarded message from Chris Klingenberg <[email protected]> -----
Date: Fri, 8 Mar 2013 02:44:13 -0500
From: Chris Klingenberg <[email protected]>
Reply-To: Chris Klingenberg <[email protected]>
Subject: Re: Compare Vector Directions?
To: [email protected]
Dear Marljin
For regression, it does matter which way the vector points.
For instance, for humans, the head goes from a shape with relatively
small face and relatively big braincase to a shape with a relatively
larger face and relatively smaller braincase with increasing overall
size, and definitely not the other way around.
The direction of regression vectors is not arbitrary, which is different
from other analyses such as PCA.
I hope that helps.
Best wishes,
Chris
On 08/03/2013 02:57, [email protected] wrote:
> ----- Forwarded message from Marlijn Noback
> <[email protected]> -----
>
> Date: Thu, 7 Mar 2013 05:52:18 -0500
> From: Marlijn Noback <[email protected]>
> Reply-To: Marlijn Noback <[email protected]>
> Subject: Compare Vector Directions?
> To: [email protected]
>
> Dear all,
>
> With enthusiasm I have tried the feature of vector direction
> comparison within MorphoJ. But there is something I do not understand.
> I sincerly hope you can help me with this issue. I am new to this
> analysis, so I am not sure how to interpret my data.
>
> I am trying to see if some of the environmental factors I am analyzing
> have similar effects on cranial shape as do changes in cranial size.
>
> I compared the following vectors:
> Regression of shape on factor A, B, C, D and E.
> Regression of shape on centroid size.
>
> And it gave me the following results:
>
> Angles (in degrees)
>
> CentSize1
> Fac.A 148.621
> Fac.B 32.194
> Fac.C 64.088
> Fac.D 76.127
> Fac.E 130.435
>
> P-values (parametric)
>
> CentSize1
> Fac.A 1.00000
> Fac.B <.00001
> Fac.C 0.00433
> Fac.D 0.08267
> Fac.E 0.99999
>
> Why is a 30 degrees angle showing a significant P value (0.0001), but
> a 150 degrees angle a P value of 1 ? I thought 150 degree angle is
> actually like 30 degrees, but then with the vectors having opposite
> signs?
> So that vectors with a 150 degree angle between them would still be
> more similar to each other (but with opposite signs) than vectors that
> have an angle of 90 degrees between them?
>
> In my opinion, the relation between Factor B and shape is very similar
> to centroid size effects, as is Factor A, although in opposite
> direction.
> All other factors have a different relation to shape.
>
> Is this the correct interpretation?
>
> I would very much appreciate your help in this.
>
> With kind regards,
>
> Marlijn Noback
>
> marlijn.noback ( at ) ifu.uni-tuebingen.de
>
> ----- End forwarded message -----
>
--
***********************************
Christian Peter Klingenberg
Faculty of Life Sciences
University of Manchester
Michael Smith Building
Oxford Road
Manchester M13 9PT
United Kingdom
Web site: http://www.flywings.org.uk
E-mail: [email protected]
Phone: +44 161 2753899
Skype: chris_klingenberg
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----- End forwarded message -----
