About xxM

xxM is a software package for multilevel structural equation modeling with complex dependent data structures.  xxM implements a modeling framework called n-Level Structural Equation Modeling (NL-SEM) and can estimate models with any number of levels.  Observed and latent variables are allowed at all levels.

Data-structures

• Hierarchically nested data (e.g., students << classrooms << schools << districts).
• Cross-classified data (e.g., students crossed within schools and neighborhoods).
• Partial nesting (e.g., only at-risk students in a classroom receive additional instruction by a tutor).
• Longitudinal data (long or wide).
• Longitudinal data with switching classification (e.g., students changing classrooms/teachers over time).
• Round-robin design (e.g., each person rates every other person in a small group).
• 360 performance evaluation data.
• A combination of above structures for different level pairs.
  

Models

• Multilevel models (MLM) with random-effects of observed variables (MLM, HLM).
• Structural equation models (SEM) with observed and latent variables at all levels. (Mplus, GLLAMM)
• Linear Mixed-Effects Models (LME) with constraints on both G and R side of the model. (lme4: lmer, SAS: HPMixed)
• Linear Growth Curve (LGC) Models.
• David Kenny’s Social Relations Model (SRM) for reciprocal dyadic ratings.
  

Estimation

• Efficient maximum Likelihood (ML) estimation.
• Profile-likelihood confidence intervals (CI).
• Fixed-to-constant and equality constraints on model parameters.
• Works well with small datasets as well.
  

Specification

• ‘If you can draw the model, you can build the model’. Graphical representation of NL-SEM models is intuitive.
• ‘If you can build a toy-model, you can build a skyscraper’. Models are constructed using a ‘building-block’ approach.
  

[size=1.285714286]Documentation

• xxM reference manual documents all commands and packaged datasets.
• xxM user’s guide provides examples of NL-SEM models.
• Additional examples of ‘live’ xxM model fitting sessions are available on the site.
  

[size=1.285714286]Support

• Discussion forum.
  

Price

• Priceless!
  

Ready?

• Begin here
  

Acknowledgement

Development of xxM was made possible by a generous grant (R305D090024) from the Institute of Education Sciences, U.S. Department of Education awarded to Paras D. Mehta.

Contact

• paras dot mehta at times dot uh dot edu
  

http://xxm.times.uh.edu/