Relates the observed values on a set of variates or factors to the results of a principal coordinates analysis (synonym of PCORELATE).
Options
COORDINATES = matrix |
Points in reduced space; no default i.e. this option must be specified |
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NROOTS = scalar |
Number of latent roots for printed output; default * requests them all to be printed |
Parameters
DATA = variates or factors |
The data variables |
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TEST = string tokens |
Test type, defining how each variable is treated in the calculation of the similarity between each unit (simplematching, jaccard, russellrao, dice, antidice, sneathsokal, rogerstanimoto, cityblock, manhattan, ecological, euclidean, pythagorean, minkowski, divergence, canberra, braycurtis, soergel); default * ignores that variable |
RANGE = scalars |
Range of possible values of each variable; if omitted, the observed range is taken |
Description
This directive was renamed PCORELATE in Release 14, but the original name of RELATE is currently still retained as a synonym. However, it may be removed in a future release.
One way of interpreting the principal coordinates obtained from a similarity matrix by PCO is by relating them to the original data variables. For each coordinate and each data variable, an F-statistic can be computed as if the variable and the coordinate vector were independent. This is not the case but, although the exact distribution of these pseudo F-values is not known, they do serve to rank the variables in order of importance of their contribution to the coordinate vector.
The DATA parameter lists the variables (variates or factors) that are to be related to the PCO results and the TEST parameter indicates their “type” as in the FSIMILARITY directive. The RANGE parameter contains a list of scalars, one for each variable in the DATA list, allowing you to standardize quantitative variates.
Qualitative variables (variates or factors with TEST settings simplematching - rogerstanimoto) are treated as grouping factors, and the mean coordinate for each group is calculated. Only 10 groups are catered for; group levels above 10 are combined. The pseudo F-statistic gives the between-group to within-group variance ratio. Missing values are excluded.
Quantitative variables (i.e. variates with other settings) are grouped on a scale of 0-10 (where zero signifies a value up to 0.05 of the range), and mean coordinates for each group are calculated. The printed pseudo F statistic is for a linear regression of the principal coordinate on the ungrouped data variate, after standardizing the data variate to have unit range; the regression coefficient is also printed.
The COORDINATES option must be present and must be a matrix. This represents the units in reduced space. Usually the coordinates will be from a principal coordinates analysis. The number of rows of the matrix must match the number of units present in the variables, taking account of any restriction.
The output from RELATE can be extensive. You may not be interested in relating the variables to the higher dimensions of the principal coordinates analysis even though you may have saved these in the coordinate matrix. The NROOTS option can request that results for only some of the dimensions are printed. If NROOTS is not specified, RELATE prints information for all the saved dimensions: that is, for the number of columns of the coordinates matrix.
Options: COORDINATES, NROOTS.
Parameters: DATA, TEST, RANGE.
See also
Directive: PCORELATE.
Commands for: Multivariate and cluster analysis.