Comparing individuals within and across situations, groups and species: metatheoretical and methodological foundations demonstrated in primate behaviour

Individuals are explored in various kinds of phenomena and contexts. But how can scientists compare individual variations across phenomena with heterogeneous properties that require different methods for their exploration? How can measurements of individual variations be made directly comparable between different studies, groups of individuals or even species? This research applies the Transdisciplinary Philosophy-of-Science Paradigm for Research on Individuals (TPS-Paradigm) to elaborate metatheoretical concepts and analytical methodologies for quantitative comparisons of individual variations within and across situations, groups and species using behavioural phenomena as examples. Established concepts from personality psychology, differential psychology and cross-cultural and cross-species research are systematically integrated into coherent frameworks and extended by adding concepts for comparing individual-specific variations (i.e., " personality ") between species. Basic principles for establishing the functional comparability of behavioural and situational categories are elaborated while considering that individuals from different groups and species often show different behaviours and encounter different situations and therefore cannot be studied with identical variables as is done in assessment-based research. Building on these principles, the chapter explores methodologies for the statistical analyses of the configurational comparability of constructs and of mean-level differences between groups and species. It highlights that situational properties are crucial for quantitative comparisons of individual variations. Fundamental differences between observational methods and assessment methods are explored, revealing serious limitations and fallacies inherent to comparisons of individuals on the basis of assessments. Implementations of the methodological principles and concepts presented are illustrated with behavioural data from four primate species (weeper capuchins, mandrills, toque macaques and rhesus macaques)