-------- Original Message -------- Subject: RE: Low sample size problem Date: Mon, 3 Nov 2008 07:52:38 -0800 (PST) From: Fred Sundstrom <[EMAIL PROTECTED]> To: <[email protected]> References: <[EMAIL PROTECTED]> Obviously a good point! What I am looking for is a way to distinguish between my groups (ie find out from which of the five groups a randomly chosen fish comes from) and so my idea was to use discriminant analysis to see how well the morphmetric data can do that for me. I am also using "specialists colleagues" to do this by eye from the same photographs, but they have not been very good at it (chimp level). So my second idea was to use the morphometric data to try and visualize the shape differences with TpsRelw using the first two RW and "teach" my colleagues (attracted by the smell of coffee and cookies...) what to look for and then have them look at my photos again. My (possibly erroneous) analysis using the first 6 RW and body length classify fish with an accuracy of 72-100 % with the group with the lowest sample size being the 100 % ones. Cheers, Fred -----Original Message----- From: morphmet [mailto:[EMAIL PROTECTED] Sent: den 3 november 2008 04:04 To: morphmet Subject: RE: Low sample size problem -------- Original Message -------- Subject: RE: Low sample size problem Date: Sat, 1 Nov 2008 17:32:37 -0700 (PDT) From: F. James Rohlf <[EMAIL PROTECTED]> Reply-To: [EMAIL PROTECTED] Organization: Stony Brook University To: [email protected] References: <[EMAIL PROTECTED]> The obvious question is what do you plan to do with the relative warp scores? If you wish to use MANOVA or CVA to test for differences between the two means then there is a sample size problem. However, you could simply compute the Procrustes distance between the two means and then do a permutation test to see whether this distance is unusually large. That test does not require a full rank covariance matrix. In many cases this test does not have as much power as the standard test but it may be sufficient in your case. ------------------------ F. James Rohlf, Distinguished Professor Ecology & Evolution, Stony Brook University www: http://life.bio.sunysb.edu/ee/rohlf
-----Original Message----- From: morphmet [mailto:[EMAIL PROTECTED] Sent: Friday, October 31, 2008 3:35 PM To: morphmet Subject: Low sample size problem -------- Original Message -------- Subject: Low sample size problem Date: Fri, 31 Oct 2008 11:34:02 -0700 (PDT) From: Fred Sundstrom <[EMAIL PROTECTED]> To: <[email protected]> Dear List I have a problem with low sample sizes and request your advice. I have used TpsDig2 to take 13 landmarks on fish from five different groups. However, in one group I only have 8 specimens and in another only 12 and unfortunately I cannot get more of these samples. I understand that I should not used all 22 partial warp scores to analyze this. My idea the is then to use the first 6 or 7 relative warps, but is this ok? Or is this is even advisable or is there a better (alternative) way of dealing with this problem of more landmarks than specimens? Any input is much appreciated! Best fishes, Fred Sundstrom -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
-- Replies will be sent to the list. For more information visit http://www.morphometrics.org -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
