Multilevel (or Hierarchical Linear) Modeling
Most developmental questions involve studying how individuals change over time and context. In particular, some common questions are: Are there intraindividual differences in change? Are there interindividual differences in this intraindividual change? How do we explain these differences? These questions cannot be properly answered with models that assume independent observations. In most cases, an individual’s behavior at one time is associated with his behavior at another time and individuals within the same context (e.g., school, peer group, family) tend to be more similar than individuals in different contexts.
Earlier approaches often ignored these dependencies (e.g., treated all family members as independent), only focused on the highest-level unit by averaging over lower observations, or only examined one observation at a time (e.g., collected data from one friend). These options can all lead to erroneous conclusions. Instead, the questions may be better addressed in a multilevel modeling (MLM) framework, which accounts for non-independent observations without losing information. These models also allow us to move beyond individual-level predictors of change to include factors at other levels.
For an introduction to multilevel modeling and how it can be used to separate average peer context from deviations in peer context, you can view my comprehensive project for my Master's of Applied Statistics degree.
Introductory resources for those interested in multilevel modeling
Introductory Texts:
Hedeker, D., & Gibbons, R.D. (2006).Longitudinal Data Analysis. Hoboken, N.J.: John Wiley & Sons, Inc.
Raudenbush, S. W., & Bryk, A. S. (2002). Hierarchical Linear Models (2nd ed.). Newbury Park, CA: Sage.
Singer, J. D., & Willett, J. B. (2003). Applied Longitudinal Data Analysis: Modeling Change and Event Occurrence. New York:
Oxford University Press.
Snijders, T.A.B., & Bosker, R. (1999). Multilevel Analysis. Thousand Oaks, CA: Sage.
Applications:
Dearing, E., McCartney, K., Taylor, B.A. (2006). Within-child associations between family income and externalizing and
internalizing problems. Developmental Psychology, 42(2), 237-252.
Kim, J.Y., McHale, S. M., Osgood, D. W., & Crouter, A. C. (2006). Longitudinal course and family correlates of sibling
relationships from childhood through adolescence. Child Development, 77(6), 1746-1761.
Websites:
Lesa Hoffman's homepage at University of Nebraska
Everything I learned about MLM started in Lesa's class when she was a postdoc at Penn State. All of her lecture materials
(including audio) are available from her homepage. Highly recommended!