Re: [MORPHMET] Re: semilandmarks in biology

2018-11-12 Thread Douglas Boyer
iological effects of interests are beforehand, > because we wouldn't know what we measured. > > M > > > -Original Message----- > From: Benedikt Hallgrimsson > Sent: Thursday, November 8, 2018 11:32 AM > To: Adams, Dean [EEOBS] ; andrea cardini < > alcard...@gm

RE: [MORPHMET] Re: semilandmarks in biology

2018-11-11 Thread Murat Maga
fects of interests are beforehand, bec= ause we wouldn't know what we measured. M -Original Message- From: Benedikt Hallgrimsson =20 Sent: Thursday, November 8, 2018 11:32 AM To: Adams, Dean [EEOBS] ; andrea cardini ; morphmet@morphometrics.org Subject: RE: [MORPHMET] Re: semilandm

RE: [MORPHMET] Re: semilandmarks in biology

2018-11-08 Thread Benedikt Hallgrimsson
logical pragmatism, but I hope some find this useful. Benedikt -Original Message- From: Adams, Dean [EEOBS] Sent: Wednesday, November 7, 2018 6:48 AM To: andrea cardini ; morphmet@morphometrics.org Subject: RE: [MORPHMET] Re: semilandmarks in biology Folks, I think it is importa

RE: [MORPHMET] Re: semilandmarks in biology

2018-11-07 Thread Adams, Dean [EEOBS]
of Ecology, Evolution, and Organismal Biology Iowa State University www.public.iastate.edu/~dcadams/ phone: 515-294-3834 -Original Message- From: andrea cardini Sent: Wednesday, November 7, 2018 4:31 AM To: morphmet@morphometrics.org Subject: Re: [MORPHMET] Re: semilandmarks in biology

Re: [MORPHMET] Re: semilandmarks in biology

2018-11-07 Thread andrea cardini
Making cool pictures has a purpose only if both the pics and the numbers behind them are accurate. It's not an aim in itself, I hope (although this is the second time I hear that one should add as many points as needed to see a nice picture). Parsimonious explanations are, to me, much more appe

Re: [MORPHMET] Re: semilandmarks in biology

2018-11-06 Thread N. MacLeod
Agreed. In addition, I think it’s important to note that, in the original implementations of the sliding algorithm, semilandmarks were slid not along the curve itself, but along tangents to the curve (= off the boundary outline). How much distortion this induces is, of course, a function of how

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

Re: [MORPHMET] Re: semilandmarks in biology

2018-11-06 Thread alcardini
Indeed one of my favourite examples where semilandmarks are really useful is a paper by Hublin, Gunz et al. (with apologies for the inaccurate ref. and mixed up order of authors) where they manage to classify as Neanderthal a piece of cranial vault found (I believe) in Belgium and possibly in the s

Re: [MORPHMET] Re: semilandmarks in biology

2018-11-06 Thread Mike Collyer
Andrea, I am intrigued by your initial comment about adding covariance that was apparently absent. I tend to think of the problem from the other perspective of not accounting for covariance that should be present. As a thought experiment (that could probably be simulated, and maybe I am not c

RE: [MORPHMET] Re: semilandmarks in biology

2018-11-06 Thread F. James Rohlf
iginal Message- From: alcardini Sent: Tuesday, November 6, 2018 12:35 PM To: F. James Rohlf Cc: mitte...@univie.ac.at; MORPHMET Subject: Re: [MORPHMET] Re: semilandmarks in biology Yes, but doesn't that also add more covariance that wasn't there in the first place? Neither l

Re: [MORPHMET] Re: semilandmarks in biology

2018-11-06 Thread alcardini
Yes, but doesn't that also add more covariance that wasn't there in the first place? Neither least squares nor minimum bending energy, that we minimize for sliding, are biological models: they will reduce variance but will do it in ways that are totally biologically arbitrary. In the examples I sh

RE: [MORPHMET] Re: semilandmarks in biology

2018-11-06 Thread F. James Rohlf
I agree with Philipp but I would like to add that the way I think about the justification for the sliding of semilandmarks is that if one were smart enough to know exactly where the most meaningful locations are along some curve then one should just place the points along the curve and computati