I would especially like to thank three friends without whom this work could hardly have been completed in its current form and timeframe: Beate Seitz, who patiently and persistently discussed the structure of the work as well as the individual ideas and theses with me, significantly contributing to ensuring that this book did not become completely chaotic and did not drift too much into various more or less interesting peripheral areas; Rainer Schnell, who willingly clarified all my small and large problems with statistics at the most inconvenient times and helped avoid many mistakes; and last but not least, Ursula Czeranski, who not only wrote the book but also assisted me in the writing process.