betweenindividual

Between-individual refers to differences that occur across individuals within a population. The term is used to describe variability attributable to differences from one person to another, as distinct from within-individual variation that arises when the same person is measured multiple times or under different conditions.

In statistics and data analysis, between-individual variance is one component of the total phenotypic variance. Mixed-effects and hierarchical models partition variance into between-individual and within-individual (or residual) components. The intraclass correlation coefficient (ICC) expresses the proportion of total variance attributable to between-individual differences.

Applications span multiple disciplines. In genetics and behavioral sciences, between-individual variation encompasses genetic and environmental influences on traits such as height, cognition, or disease risk. In pharmacology and medicine, inter-individual (between-subject) variability affects drug exposure and response, contributing to personalized medicine approaches. In psychology and epidemiology, it helps explain observed differences in behavior, health outcomes, and risk profiles across a population.

Measurement and interpretation involve distinguishing true differences between people from measurement error or sampling variation. Careful study design and appropriate statistical models are used to decompose variance, estimate heritability, and quantify effect sizes associated with individual differences.

Terminology varies by field. Between-individual is often used interchangeably with inter-individual or interindividual. In many contexts, especially clinical and pharmacological research, between-subject or inter-individual terms are common. Consistency within a work is recommended to avoid ambiguity.