Excerpt from the PDF:
With grouping classifications, in contrast, one’s starting point is a collection of individual units of some given type—whether people, houses, shopping centers, etc. One then selects some given variable—one that can be measured on a continuous scale (e.g., ratio, interval, percent, etc.)—and then determines for each individual (or a sample of same) its numerical ―value on that variable. One can then either ―feed these numbers into a grouping program (univariate) or—more typically—do the same for a series of other variables, and then feed the resulting numbers into a grouping program (multivariate). In either case the grouping program will identify ―natural groups/categories, with these groups, however, varying in their degree of internal ―closeness. That is, with some groups the individual members will be similar one to another to a very high degree, but with other groups the degree of similarity will vary. In fact, if one wishes, one can take a given category identified by the grouping program and subject its members to a grouping program—thereby identifying subgroups.
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About the author: Al Thompson works (data management) for an Engineering (Avionics) firm in Milwaukee. Click here to mail him.