[MORPHMET] Multivariate Analysis of Genotype-Phenotype Association

2016-02-25 Thread mitte...@univie.ac.at
I would like to announce a new paper, of which the early view pdf is already online. Mitteroecker P, Cheverud JM, Pavlicev M (2016) Multivariate Analysis of Genotype-Phenotype Association. Genetics http://www.genetics.org/content/early/2016/02/18/genetics.115.181339 It offers an exploratory

Re: [MORPHMET] Sliding Semilandmarks

2016-02-21 Thread mitte...@univie.ac.at
As Michael described, the average shape configuration affects the sliding when used as reference for the TPS; the final configurations thus are sample-dependent. However, if the curves/surfaces are covered densely enough by the semilandmarks (e.g., to avoid that a semilandmark can slide away

[MORPHMET] Postdoc and Ph.D. position at the Univ. of Vienna on the modelling of developmental canalization in

2016-08-12 Thread mitte...@univie.ac.at
In the working group of Philipp Mitteroecker in the Department of Theoretical Biology, University of Vienna, a two-year postdoc position and a three-year Ph.D. position are vacant. We are searching for enthusiastic persons, who are dedicated to interdisciplinary research in biology and

[MORPHMET] PhD position in biological anthropology and morphometrics

2017-01-25 Thread mitte...@univie.ac.at
We seek a PhD student for a three-year position in Vienna, working on the morphometrics of human pelvises in relation to childbirth and motherhood: www.oeaw.ac.at/fileadmin/subsites/Jobs/Job_offer_VAMOS_PhD_position_1_.pdf Best, Philipp Mitteroecker -- MORPHMET may be accessed via its

[MORPHMET] Re: Does a research sample need to be normally distributed (male/female ratio) for PCA?

2017-05-25 Thread mitte...@univie.ac.at
As an exploratory technique, PCA makes no distributional assumptions; it is used to explore the empirical distribution of the data. The sample does not need to be balanced with regard to sex or other grouping variables, but larger groups have a stronger effect on the PCA than smaller groups.

Re: [MORPHMET] Re: number of landmarks and sample size

2017-06-02 Thread mitte...@univie.ac.at
I think a few topics get mixed up here. Of course, a sample can be too small to be representative (as in Andrea's example), and one should think carefully about the measures to take. It is also clear that an increase in sample size reduces standard errors of statistical estimates, including

[MORPHMET] Re: number of landmarks and sample size

2017-05-31 Thread mitte...@univie.ac.at
Adding more (semi)landmarks inevitably increases the spatial resolution and thus allows one to capture finer anatomical details - whether relevant to the biological question or not. This can be advantageous for the reconstruction of shapes, especially when producing 3D morphs by warping dense

[MORPHMET] Open call for a "Professor of Theoretical Evolutionary Biology" at the University of Vienna

2018-04-05 Thread mitte...@univie.ac.at
Dear morphometrics community, Perhaps this call is of interest to some of you. Best, Philipp At the Faculty of Life Sciences of the University of Vienna the position of a "University Professor of Theoretical Evolutionary Biology" is to be filled. The advertised professorship shall cover

Re: [MORPHMET] Re: semilandmarks in biology

2018-11-06 Thread mitte...@univie.ac.at
Yes, it was always well known that sliding adds covariance but this is irrelevant for most studies, especially for group mean comparisons and shape regressions: the kind of studies for which GMM is most efficient, as Jim noted. If you consider the change of variance-covariance structure due to

[MORPHMET] Re: Are more semi landmarks better??

2018-11-06 Thread mitte...@univie.ac.at
I'd like to respond to your question because it comes up so often. As noted by Carmelo in the other posting, a large number of variables relative to the number of cases can lead to statistical problems. But often it does not. In all analyses that treat each variable separately - including the

[MORPHMET] Re: semilandmarks in biology

2018-11-06 Thread mitte...@univie.ac.at
I agree only in part. Whether or not semilandmarks "really are needed" may be hard to say beforehand. If the signal is known well enough before the study, even a single linear distance or distance ratio may suffice. In fact, most geometric morphometric studies are characterized by an