It was the precursor of what was later known as the Gifi System, which is a large reorganization of descriptive multivariate analysis techniques in such a way that they apply both to numerical and non-numerical data. That covers regression and principal components analysis, factor analysis, all those techniques in one common framework and ultimately in a series of computer programs as well. My dissertation was basically the first programmatic statement of that program. The Gifi project itself ran until about 1990, I left in 1987, but there was still some ends to wrap up and the Data Theory group in Leiden that still existed at the time, wrapped up those loose ends. They produced a book, the final version of the Gifi book. — Interview of Jan de Leeuw by Lisa Wijsen
I was surprised to learn that he’s still publishing peer-reviewed papers and I was also very impressed to see that he’s still hard at work on working papers and books. h/t