From persons to general principles: Methodological decisions for idiographic and nomothetic research

Research in psychology can have various foci, ranging from the psychological dynamics of single individuals to the generalization across individuals, often termed idiographics and nomothetics, respectively. However, terminological ambiguities have limited communication clarity about idiographics and nomothetics. Importantly, whether studies are suitable for idiographic and/or nomothetic inferences is not categorical but rather a matter of degree. Therefore, we propose a list of concrete, better-defined methodological aspects characterizing individual studies. Specifically, we highlight 16 different decisions researchers have to make pertaining to (1) research question, (2) research design, and (3) analyses and interpretation. These decisions are introduced with a focus on personality psychology but apply to psychological research broadly. We discuss the different decisions with an emphasis on their relation to idiographic and nomothetic inferential goals. Rather than providing specific recommendations, we emphasize the importance of aligning the methodology of a given study with the research question and theory. Overall, this overview seeks to help researchers make relevant decisions more intentionally to help them tailor their studies to their inferential goals.Psychological research can be focused on specific individuals (often termed idiographic) or on generalization across individuals (often termed nomothetic). However, various definitions of these terms exist in the literature. Moreover, multiple different aspects of a study affect whether it allows us to understand a specific person and/or whether it allows generalization across people. To characterize individual psychological studies in a more detailed way, we propose a list of 16 decisions researchers have to make. These decisions include aspects of (1) the research question, (2) the research design, and (3) the analyses and interpretation. We discuss how these decisions are related to idiographics and nomothetics. Moreover, we emphasize the importance of a close match between the questions a study seeks to answer and the methodology used in the study. The proposed list of decisions can be used by other researchers to characterize existing studies as well as to plan new studies.