| Summary: | This book is dedicated to the memory of Gis©·le Mersch whose life ended prematurely in June 2002. Back in the 1970s, when few people were using them, Gis©·le introduced me to the arcane secrets of then advanced m- tivariate statistical methodologies. I was already involved in more classical statistical studies undertaken at Paris Observatory with Jean Jung: developing and applying maxim- likelihood algorithms to stellar photometric and kinematic data in order to derive absolute luminosities, distances and velocities in the solar neighb- hood. But what could be envisaged with those methodologies was something of another dimension: for the first time, I could really see how to extract information from massive amounts of data without calling for elaborated physical or mechanical theories. Several pioneering applications were developed under Gis©·leÌÌ"-Ì"-¿ "s guidance and with her collaboration to study the delicate interface between spect- scopic and photometric data. Thus errors in spectral classifications were investigated as well as predictions of spectral classifications from pho- metric indices (see Heck 1976, Heck et al. 1977, Heck & Mersch 1980 and Mersch & Heck 1980), with very interesting results for the time. Gis©·le also took part in studies of period determination algorithms (see Mersch & Heck 1981, Manfroid et al. 1983 and Heck et al. 1985).
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