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Date:         Thu, 27 Jul 2006 16:14:12 +0100
Reply-To:     "Allan Reese (Cefas)" <allan.reese@cefas.co.uk>
Sender:       "SPSSX(r) Discussion" <SPSSX-L@LISTSERV.UGA.EDU>
From:         "Allan Reese (Cefas)" <allan.reese@cefas.co.uk>
Subject:      Two-step cluster
Content-Type: text/plain; charset="iso-8859-1"

I'm trying twostep cluster in version 13. The documentation states that it will select "between 1 and the maximum" number of clusters using the Information Criterion. I assume it is looking for a maximum AIC/BIC so find this output (apologies that column headings don't line up with values) inconsistent with it reporting two clusters for this dataset. This seems so obvious that I'm probably overlooking the obvious.

Auto-Clustering Number of Clusters Akaike's Information Criterion (AIC) AIC Change(a) Ratio of AIC Changes(b) Ratio of Distance Measures(c) 1 42679.177 2 29736.437 -12942.740 1.000 3.076 3 25584.939 -4151.498 .321 1.444 4 22736.637 -2848.302 .220 1.751 5 21145.674 -1590.963 .123 1.008 6 19567.475 -1578.199 .122 1.515 7 18554.435 -1013.040 .078 1.257 8 17765.615 -788.819 .061 1.034 9 17005.491 -760.125 .059 1.151 10 16356.395 -649.095 .050 1.150 11 15802.853 -553.542 .043 1.305 12 15398.294 -404.559 .031 1.167 13 15063.487 -334.807 .026 1.095 14 14765.135 -298.352 .023 1.084 15 14496.451 -268.684 .021 1.225 a The changes are from the previous number of clusters in the table. b The ratios of changes are relative to the change for the two cluster solution. c The ratios of distance measures are based on the current number of clusters against the previous number of clusters.

If there is in fact only one cluster, this may explain why the next output lists all the variables in their name order, though the command description states they "will be sorted by the importance rank of each variable."

The documentation for this command is very sparse, so I'd appreciate feedback from other users. The menu generates syntax for "twostep cluster" followed by "aim" but I am unable to trace any documentation for AIM.

Allan

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