A group of eleven Ph.D. candidates from seven countries--Robin Cowan, Andrew Foster, Nedka Gateva, William Hodges, Arno Kitts, Eva Lelievre, Fernando Rajulton, Lucky Tedrow, Marc Tremblay, John Wilmoth, and Zeng Yi--worked together at IIASA from June 17 through September 6, 1985, in a seminar on population heterogeneity. The seminar was led by the two of us with the help of Nathan Keyfitz, leader of the Population Program, and Bradley Gambill, Dianne Goodwin, and Alan Bernstein, researchers in the Population Program, as well as the occasional participation of guest scholars at IIASA, including Michael Stoto, Sergei Scherbov, Joel Cohen, Frans Willekens, Vladimir Crechuha, and Geert Ridder. Susanne Stock, our secretary, and Margaret Traber managed the seminar superbly.
Each of the eleven students in the seminar succeeded in writing a report on the research they had done. With only one exception, the students evaluated the seminar as "very productive"; the exception thought it was "productive". The two of us agree: the quality of the research produced exceeded our expectations and made the summer a thoroughly enjoyable experience. We were particularly pleased by the interest and sparkle displayed in our daily, hour-long colloquium, and by the spirit of cooperation all the participants, both students and more senior researchers, displayed in generously sharing ideas and otherwise helping each other.
One of the best of the research reports produced and probably the most original is the report by John Wilmoth that appears in this working paper. Building on some of the work on the mathematics of population surfaces, on the use of shaded contour maps for displaying population surfaces, and on Italian mortality that had been started at IIASA by the two of us and W. Brian Arthur, Bradley A. Gambill, and Graziella Caselli, Wilmoth developed an approach for analyzing age, period, and cohort effects that shows considerable promise for further development and application. This report thus exemplifies the productive role IIASA can play in bringing together diligent, creative scholars from different countries and disciplines