Automatic clustering

Receiving only the table, and returning the groups — four decisions that all commit the result

Mind map of chapter 26: the three methods of the part differ by the information they receive — factor analysis receives the table and returns axes, discriminant analysis also receives the groups, clustering receives only the table and returns the groups. Clustering requires four decisions: proximity, quality criterion, construction strategy, stopping rule. Minimising I_W and maximising I_B are one problem. The procedure converges to a local minimum: the starting point decides the end point. A computed partition has no general reason to recover a declared one; here it does, and the structure is stable where the detail is not.