Hierarchical Linear Models (HLM), also known as multilevel modeling, are statistical techniques used to analyze data that has a hierarchical or nested structure.
HLM involves at least two levels: individual observations and group-level influences, with a mathematical representation that considers predictors, random effects, and error terms.
Assumptions of HLM include normality of residuals, homoscedasticity, and independence of observations, with random effects following a normal distribution.
HLM is widely used in education, psychology, healthcare, and social sciences due to its ability to handle unbalanced data structures, incorporate fixed and random effects, and model complex real-world scenarios.