Maria Grazia Pittau

Exploring patterns of income polarization using siZer

Abstract

Tendency towards a more income polarized society can be explored by a graphical tool, the SiZer, originally introduced by Chaudhuri and Marron (1999, 2000).

The assessment of significant of zero crossings of derivatives helps determine which features in the family of empirical kernel distributions are statistically significant for given bandwidths.

The SiZer approach is modified in this paper for handling adaptive kernel estimations, more suitable for income data. SiZer maps are related to changes in the shape of the distributions and to the degree of income polarization.

Using this method, this paper investigates the vanishing middle income class hypothesis in Italy, which is claimed to have taken place at the beginning of the decade.

Journal of Quantitative Economics,  5, 101--111, 2007.