This book is dedicated to the memory of Gisèle Mersch whose life ended prematurely in June 2002. Back in the 1970s, when few people were using them, Gisèle introduced me to the arcane secrets of then advanced multivariate statistical methodologies. I was already involved in more classical statistical studies undertaken at Paris Observatory with Jean Jung: developing and applying maximumlikelihood algorithms to stellar photometric and kinematic data in order to derive absolute luminosities, distances and velocities in the solar neighborhood
