Factor Preselection and Multiple Measures of Dependence

Factor selection or factor reduction is carried out to reduce the complexity of a data analysis problems (classification, regression) or to improve the fit of a model (via parameter estimation). In data mining there are special needs for a process by which relevant factors of influence are identified in order to achieve a balance between bias and noise. Insurance companies, for example, face data sets that contain hundreds of attributes or factors per object. With a large number of factors, the selection procedure requires a suitable process model. A process like that becomes compelling once data analysis is to be (semi) automated.We suggest an approach that proceeds in two phases: In the first one, we cluster attributes that are highly correlated in order to identify factor combinations that—statistically speaking—are near duplicates. In the second phase, we choose factors from each cluster that are highly associated with a target variable. The implementation requires some form of non-linear canonical correlation analysis. We define a correlation measure for two blocks of factors that will be employed as a measure of similarity within the clustering process. Such measures, in turn, are based on multiple indices of dependence. Few indices have been introduced cf. Wolff (Stochastica 4(3):175–188, 1980), ‘Few indices have been introduced in the literature’. All of them, however, are hard to interpret if the number of dimensions considerably exceeds two. For that reason we come up with signed measures that can be interpreted in the usual way.