Writing a book is not possible without the generous input of many people. It is a pleasure to have the opportunity to thank at least some of these people. Prof. Dr. Jochen Michaelis, the supervisor of my dissertation, taught me how to do economic analysis and initiated my interest in labour market is sues. Discussions with him have always been enlightening and have greatly improved the analysis in this book. Moreover, he always encouraged me when I experienced a slump in my motivation. He never lost his calmness and good temper, not even in situations when my need for discussion must have...