I would add to the fine advice so far that you can increase the iterations in K-means (maybe from the default of 10 to 20). This will help stabilize the problem of sort dependence.

Best,

Keith www.keithmccormick.com

On Mon, May 17, 2010 at 12:34 PM, john wurst <jwurst@sdr-consulting.com>wrote:

> Another approach is to use both hierarchical and K-Means (tandem > approach). Run hierarchical (Wards is a common method) and use the group > centroids as the starting seeds for K-means. > > -----Original Message----- > *From:* SPSSX(r) Discussion [mailto:SPSSX-L@LISTSERV.UGA.EDU]*On Behalf Of > *Art Kendall > *Sent:* Monday, May 17, 2010 11:54 AM > *To:* SPSSX-L@LISTSERV.UGA.EDU > *Subject:* Re: K-Means Cluster Analysis > > k-means is very dependent on the order the cases are in. One expects > slightly different results with addition or omission of a few cases or > changes in the sort order of the cases. > That is why I have long recommended that a user sort the cases in a few > random orders and checks the consistency of the assigned cluster > memberships. > > > *Are you getting different results with identical input?* > > Also TWOSTEP is a step up from the older k-means approach. > > What is the nature of your data? Kinds of variables? relative independence > of the variables? what kind of entity is the case? > > Art Kendall > Social Research Consultants > > On 5/17/2010 10:15 AM, Courtney M. Cronley wrote: > > I am running a K-means cluster analysis with 12 clusters, and I keep getting different clusters. For example, yesterday Cluster 2 had two cases in it. Today Cluster 2 has one case in it. Any ideas about why this is the case? > > Thanks in advance for any advice that anyone can offer. > > Best, > > Courtney Cronley, Ph.D. > Postdoctoral Associate > Center of Alcohol Studies > Rutgers Universitycronley@rci.rutgers.edu > > ===================== > To manage your subscription to SPSSX-L, send a message toLISTSERV@LISTSERV.UGA.EDU (not to SPSSX-L), with no body text except the > command. To leave the list, send the command > SIGNOFF SPSSX-L > For a list of commands to manage subscriptions, send the command > INFO REFCARD > > > > ===================== To manage your subscription to SPSSX-L, send a > message to LISTSERV@LISTSERV.UGA.EDU (not to SPSSX-L), with no body text > except the command. To leave the list, send the command SIGNOFF SPSSX-L For > a list of commands to manage subscriptions, send the command INFO REFCARD > >