Hello, I intend to use MetaNMDS on ordinal data and was wondering if there are any guidelines and examples what to do (and especially what not to do). At the moment my design decisions are to use an Euclidian distance matrix (since I use already ordinal data anything more complecated seems to be inappropiate). I want to test dependencies on environmental factors post-hoc. Are there any thoughts, articles or anything else to help a newby in ordinations on that subject? Frank Frank Berninger Associate professor Forest Ecology Department of Forest Sciences POBOX 27 00014 University of Helsinki
MetaNmds and ordinal data
2 messages · Frank Berninger, Sarah Goslee
1 day later
Hi Frank, On Thu, Mar 26, 2015 at 3:37 AM, Frank Berninger
<frankberninger at gmail.com> wrote:
Hello, I intend to use MetaNMDS on ordinal data and was wondering if there are any guidelines and examples what to do (and especially what not to do). At the moment my design decisions are to use an Euclidian distance matrix (since I use already ordinal data anything more complecated seems to be inappropiate). I want to test dependencies on environmental factors post-hoc. Are there any thoughts, articles or anything else to help a newby in ordinations on that subject?
While it's common to treat ordinal data like interval data, that can be a problem for distance-based tests if the difference between 0 and 1, for example, is substantially different than the difference between 10 and 11: both will have the same Euclidean distance, even though they aren't equally dissimilar. There are various alternatives, including ranked distances, Gower dissimilarity, etc. Without knowing anything else about your data or hypotheses, it's impossible to give you advice beyond spending some time with the many journal articles in the Journal of Vegetation Science discussing multivariate analyses of ordinal data. Sarah
Sarah Goslee http://www.functionaldiversity.org