Multilevel Modeling

Multilevel modeling (MLM) is a regression-based approach for handling nested and clustered data. Nested data (sometimes referred to as person–period data) occurs when research designs include multiple measurements for each individual, and this approach allows researchers to examine how participants differ, as well as how individuals vary across measurement periods. A good example of nested data is repeated measurements taken from people over time; in this situation, the repeated measurements are nested under each person. Clustered data involves a hierarchical structure such that individuals in the same group are hypothesized to be more similar to each other than to other groups. A good example of clustered data is the study of classrooms within different schools; in this situation, classrooms are embedded within the schools. Standard ...