I have a 127-question survey with 6-level likert type answers. With EFA I have kept 56 items and got 8 factors. With CFA (on sample not used in EFA) I confirmed these factors. so far all good.
When I tried to do cluster analysis, with 8 all factors I did not get clear solution (I used SAS, and used the CCC and pseudo F and T statistics indicators to judge the number of clusters; ccc: Cubic Clustering Criterion).
When I used 7 factors, I got a clearly solution of 3 clusters. All three indicators (CCC, pseudo F and statistics) suggested cluster number of 3. And further analysis with 3 clusters looks very reasonable to us.
my question is: Do I must use all 8 factors from EFA/CFA to do cluster analysis?