This question refers to the proper way to analyze 4-Dimensional data sets using geometric morphometrics.
The data that I am talking about are a series of 3D data measured from two different groups at regular time intervals - essentially changing shapes during growth. The question I would like to address is if the same types of changes in shape over time occur in both groups. In terms of a simple bivariate analysis each group can be characterized by shape/time and the analysis would compare the shape/time slopes between the two groups. The complication is that "shape" is multivariate landmark data and that there is no reason to believe that shape change would have a quasi-linear relationship with time. So, my question is how to approach these data. Do I conduct a Procrustes analysis of the entire data set including the time, essentially a superimposition of 4D data, and compare groups with these numbers - treating the time value as just another dimension (XYZT coordinates)? Or, do I conduct a Procrustes superimposition of the 3D landmark data first and then re-associate them with their time values? Or, is there a third way to go? The problem here is similar to the setup described by Dean and Cerney in their Journal of Biomechanics (2007) article, although I am not entirely certain that their solution applies to this case. Maybe it does, but right now, it's a little confusing. I am not sure which way is correct, and I would appreciate the advice of the group. Either way I go, I see this analysis as a MANOVA with repeated measures of shape using time as the independent variate. I would like to be able to set this up as a resampling analysis, but I can't think how I would do that with a repeated measures design. Again, any help would be appreciated. On an aside, I submitted the 4D data as an NT-SYS file to Morpheus, and it plotted the data just fine. I'm not sure what the plot means (a 2D summary of a 4D data set), but I thought it was interesting that the program still did something. Morphologika went the more expected route and refused to accept 4D data. Thomas M. Greiner, Ph.D. Assistant Professor of Anatomy Dept. of Health Professions University of Wisconsin - La Crosse 1725 State Street La Crosse, WI 54601 USA Phone: (608) 785-8476 Fax: (608) 785-8460 -- Replies will be sent to the list. For more information visit http://www.morphometrics.org
