intraklustkorrelation
Intraklustkorrelation, often abbreviated ICC, is a statistic used to describe how strongly units within the same cluster resemble each other. It measures the proportion of total variance in an outcome that is attributable to differences between clusters rather than within clusters. ICC is central to clustered study designs, multilevel models, and meta-analytic approaches, as it informs the degree of similarity of observations inside the same group.
In a simple random-intercept model, Var(Y) can be decomposed into between-cluster and within-cluster components: Var(Y) = σ²_between
Estimation methods include linear mixed-effects models for continuous outcomes and generalized linear mixed models for non-normal
A key implication of the ICC is its effect on study design. The design effect is DEFF
Applications of intraklustkorrelation include education (students within schools), healthcare (patients within clinics), and survey research with