Using SAS PROC MIXED to Fit Multilevel Models, Hierarchical Models, and Individual Growth Models

Key Points

• Provide a comprehensive methodological guide and tutorial on using the SAS PROC MIXED procedure to specify, fit, and interpret multilevel, hierarchical linear, and individual growth models.
• Demonstrates model parameterization, syntax specification, and covariance structure selection using SAS PROC MIXED for nested and longitudinal designs.
• Illustrates the translation of multilevel equations into corresponding statistical software code for fixed and random effects.
• Establishes that PROC MIXED effectively estimates parameters for two-level hierarchical models and longitudinal growth trajectories within a single general linear mixed-model framework.
• Provides practical syntax templates and output interpretations for evaluating variance components, random slopes, and fixed effects in behavioral research.