Comparative personality research: Methodological approaches

hi the broadest sense, personality refers to stable inter-individual variability in behavioural organisation within a particular population. Researching personality in human as well as nonhuman species provides unique possibilities for comparisons across species with different phylogenies, ecologies and social systems. It also allows insights into mechanisms and processes of the evolution of population differences within and between species. The enormous diversity across species entails particular challenges to methodology. This paper explores theoretical approaches and analytical methods of deriving dimensions of inter-individual variability on different population. levels from a personality trait perspective. The existing diversity suggests that some populations, especially some species, may exhibit different or even unique trait domains. Therefore, a methodology is needed that identifies ecologically valid and comprehensive representations of the personality variation within each population. I taxonomise and compare current approaches in their suitability for this task. I propose a new bottom-up approach-the behavioural repertoire approach-that is tailored to the specific methodological requirements of comparative personality research. Initial empirical results in nonhuman primates emphasise the viability of this approach and highlight interesting implications for human personality research. Copyright (C) 2008 John Wiley & Sons, Ltd.