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September 2008


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Liza Rovniak <[log in to unmask]>
Reply To:
Classification, clustering, and phylogeny estimation
Wed, 3 Sep 2008 15:39:57 -0700
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I am hoping someone here can help me with a "how to" question on running
McIntyre and Blashfield's (1980) nearest-centroid evaluation procedure
to validate the stability of my cluster analysis solution. I am a newbie
to cluster analysis, so this is my first time running this procedure. 


I have a sample of  about 900 observations and have randomly split the
sample in two (Sample A and Sample B). I conducted hierarchical cluster
analysis and then calculated the centroid vectors for a 3-cluster
solution on each of these two subsamples (i.e., steps 1 through 4 of
McIntrye and Blashfield's evaluation technique). 


Step 5 of McIntrye and Blashfield's technique is to calculate "the
squared Euclidean distance for each of Sample B's objects from each of
the centroids of Sample A," and Step 6 is to assign "each object  in
Sample B to the closest centroid vector." At this point, I am not sure
what buttons to press in SPSS to complete the analysis. One possibility
I tried is to use K-means cluster analysis to achieve these two steps,
but K-means uses simple Euclidean distance (not squared Euclidean
distance as recommended by McIntyre and Blashfield) to assign the
observations to clusters. Is this okay? (someone told me it was, but I
just want to double-check).  I would greatly appreciate any guidance on
what buttons to press in SPSS/appropriate syntax to complete steps 5 and
6 of this analysis. 


Thank you.


Liza Rovniak


Liza S. Rovniak, PhD, MPH

Adjunct Assistant Professor

Center for Behavioral Epidemiology & Community Health

Graduate School of Public Health, San Diego State University

San Diego, CA 92123

Phone: 858-505-4770, ext. 152; Fax: 858-505-8614

Email: [log in to unmask]


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