The source of a river is often difficult to find. More often than not, rivers originate from multiple small-water sources and creeks that trickle down, often underground, until they merge in larger streams and eventually become a river. The situation is not much different for scientific disciplines. Cross-cultural psychology started about forty years ago as a separate discipline, but its intellectual parental disciplines are much older. Since its inception, the field has grown considerably. Indeed, it may even be fair to argue that, as a scientific discipline, cross-cultural psychology has come of age. There are a few journals (such as the Journal of Cross-Cultural Psychology, the Journal of Cross Cultural Management and the International Journal of Intercultural Relations) that are entirely devoted to the field, and there are many more journals that publish cross-cultural studies on a regular basis. All mainstream psychology journals have published cross-cultural studies. In addition, there is a professional organisation that is exclusively devoted to cross-cultural psychology (the International Association for Cross-Cultural Psychology). Both the association and the Journal of Cross-Cultural Psychology were launched at about the same time forty years ago, which seems to provide sufficient institutional reasons for defining this as the beginning of the discipline.

There is a time-honoured tradition in academia of writing a liber amicorum for a senior at the end of a typically successful career in university. But, as we know from ethnography, even rituals with a seemingly similar purpose come with much cultural variation. The idea of a combination of a universal theme and local variations is applicable to this book in a double sense.

First, it explains why the book has been written. Ype Poortinga is no longer Professor of Cross-Cultural Psychology at Tilburg University, the Netherlands, but has become an emeritus professor. This book is a liber amicorum dedicated to Ype as the founding (and still active) father of cross-cultural psychology in Tilburg and a key international player in the field. Yet, we deviate from the implicit recipe of the liber amicorum. This variation is mainly inspired by Ype's preferences. We think that a book with an up-to-date overview of modern theories and models in cross-cultural psychology will give him much more pleasure than a selection of chapters with anecdotes from his colourful past, in however lively a manner these are described. History is important in the book, not as anecdotes, but as references to the state of cross-cultural psychology forty years ago and to its current state. We take stock of cross-cultural psychology of the last forty years, which roughly spans Ype's professional career as well as the rise of empirical cross-cultural psychology.

The chapter starts from the above quotation by Tom Smith, who complained in a book on cross-cultural survey methods that comparability issues in cross-cultural surveys are more often mentioned than addressed. In a similar vein, Bollen, Entwistle and Alderson (1993) found in a meta-analysis of macrocomparative studies that equivalence is infrequently addressed. The situation in cross-cultural psychology is not much different; there is a widely acknowledged, shared awareness of potential pitfalls of direct cross-cultural score comparisons, but the sensitivity for the issue is insufficiently accompanied by tests of instrument adequacy in a specific study. It was argued in the first chapter by the editors that method issues are at the core of cross-cultural psychology. This chapter discusses one specific method issue, namely possible sources of bias in cross-cultural studies and the ramifications of bias for the cross-cultural comparability of scores. The editors mentioned in their chapter that the methodological problems of cross-cultural studies were already described seventy years ago and that many empirical researchers, methodologists and psychometricians have tried to tackle these problems. The question is addressed here to what extent we have advanced in this field. The present chapter deals with the question of how we should evaluate the current situation with regard to the study of bias.