Project related mailbag - Friday

Got the following emails and also postiong my responses:

Dear Professor,

I tried to do cluster analysis for Q 21 and 7. I could not find cluster centroid data (as discussed in the lec 8) under any of the three classification methods. Can you please guide me towards proper menu option?

Regards,

My reply:

>> I tried to do cluster analysis for Q 21 and 7.

What does that mean exactly? Hope you filtered out respondents that don’t belong to the target popn before commencing on a factor analysis of Q21 and 7 before commencing cluster analysis using the factor scores.

>> I could not find cluster centroid data (as discussed in the lec 8) under any of the three classification methods.
Once you have Cluster membership, merely sort the segments by cluster number and find variable means for each cluster. That is the set of cluster centroids.

>> Can you please guide me towards proper menu option?
I would if I knew. Fact is, SPSS is new to me. I would suggest exploring the menu option yourself. Else, compute cluster centroids as mentioned above.

Sudhir

Then this one:

Dear Prof. Voleti,

Needed a clarification from you on factor and cluster analysis.

Can we use nominal or ordinal variable for factor analysis? From lecture slides, I understand that we cannot use such variable for factor analysis.

If we want to use nominal or ordinal variables for cluster analysis, but want to use factor analysis to reduce the number of variables first, how can we do this? If we cannot do this, then can we use such variables directly for cluster analysis?

Regards,

And my reply:

Nonmetric variables cannot be used for factor analysis. Nominal variables will have to be first transformed into dummy variables before they can be cluster analyzed.

My suggestion: Use only metric variables for factor and cluster analyses. Later, after clusters have been formed, use the nominal variables to characterize the segments.

Sudhir

Hope that helped.