Analysis of instability of ordinations
Tausch et al. (Journal of Vegetation Science, 6,
897-902; 1995) found out that some programs for Correspondence
Analysis were dependent on the input order of species and sites.
Peter Minchin and me have studied the performance of CANOCO. We
explain the main results of our studies in a an article in Journal
of Vegetation Science 8, 447-454; 1997 (you can have
a look at its abstract). The
main results are:
- CANOCO is unstable as well, but not as badly as the software
studied by Tausch et al.
- Too lax convergence criteria are the main source of instability
in orthogonal CA.
- An order dependent bug in rescaling
is the main source of instability detrended CA.
What to do?
You will find most detailed information in our article in Journal
of Vegetation Science 8, 447-454, 1997. In this
web page you can find some software to help to solve the problems
of instability. You may take the following steps in analysing
the stability of your application:
- Those users who have the CANOCO source files and a FORTRAN
compiler can make the changes themselves following the guidelines
in our article (i.e., using stricter convergence criteria
and correcting the rescaling bug).
- Users should check whether the current version of CANOCO is
sufficiently stable for their data sets by getting the programs
CEPSHUFL and SOLCOMP from this
web server. For many data sets the results may be adequate. If
the results are deemed unstable, users may take one of the following
- For CA, use our program CASVD.
- For DCA, use our debugged, strict version of DECORANA.
- Bruce McCune informed us that the new release of their PC-ORD
software uses now "superstrict" convergence criteria,
and DCA bug is corrected. More on their web pages.
[Note added 29/8/97]
- Cajo ter Braak informed us that the current version 3.15 of
CANOCO uses "strict" convergence criteria and the DCA
bug is corrected. More detailed description can be found through
official CANOCO v3.15 web pages.
These pages include some further discussion on CANOCO instability,
and challenge some of the theses. Here is our response to Cajo ter Braak
on rescaling bug [Note added 5/11/1997, updated 9/3/98]
Canoco for Windows 4.0 is now available. Check CfW homepage [Note
Go to the frontpage of Jari Oksanen