wbCorr - Bivariate Within- and Between-Cluster Correlations

Separates supplied variables into within- and between-cluster components and calculates bivariate correlations for each level separately. The centered-score decomposition corresponds to commonly used between- and within-cluster correlations discussed by Tu et al. (2025) <doi:10.1002/sim.10326>. The package is also motivated by the distinction between within- and between-person variation described by Curran and Bauer (2011) <doi:10.1146/annurev.psych.093008.100356> and by Hamaker (2024) <doi:10.1080/00273171.2022.2155930>. The package is intended for longitudinal or otherwise clustered data where researchers need transparent correlation matrices before fitting more complex multilevel models.