Dear Alexi,
You can compare grids with only the constructs or the elements matched.
Here's a quick synopsis of how Slater computed a single statistic indicating the
degree of similarity among matched elements across any number of grids:

The general correlation among grid elements can range, in principle, from 0 to
1, but it can yield a negative result with genuine data. It is computed as the
intraclass correlation coefficient among the element angles of the grids being
compared. The first step in computing this value then is to compute the element
correlation matrices for the individual grids. These correlations are then
converted to angular distances in radians. An Analysis of Variance (ANOVA) is
then conducted on these matrices of angular distances from which the intraclass
correlation coefficient is finally computed.

Another strategy is to use Generalized Procrustes Analysis, which was
pioneered
by Gower in the 1970's. Here are a few references:

Dijksterhuis, G. B., Gower, J. C. (1991/2). The interpretation of generalized
procrustes analysis and allied methods. Food quality and preference, 3, 67-87.

Fewer, L. J., Howard, C., & Shepherd, R. (1997). Public concerns in the United
Kingdom about general and specific applications of genetic engineering: Risk,
benefit, and ethics. Science, Technology, & Human Values, 22, 98-124.

Gower, J. C. (1975). Generalized procrustes analysis. Psychometrika, 40,
33-51.

I also wrote a short encyclopedia entry for Generalized Procrustes Analysis.
If you are interested in receiving a pre-print of this entry, please send me a
private e-mail at jgrice@..., and I'll be happy to send you a copy in MS
Word format.

Other approaches may be available, but these are the two I am familiar with.
Best wishes,
James





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Idiogrid Software
Box 1028
180 Student Union
Stillwater, OK 74078-7037
http://www.idiogrid.com

James W. Grice, Ph.D.
Associate Professor
http://psychology.okstate.edu/faculty/jgrice/
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