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umx is a structural equation modeling package designed to make SEM easier, from building, to modifying and reporting.

Please cite as:


Timothy C. Bates, Michael C. Neale, Hermine H. Maes, (2019). umx: A library for Structural Equation and Twin Modelling in R. Twin Research and Human Genetics, 22, 27-41. DOI:10.1017/thg.2019.2

umx includes high-level functions for complex models such as multi-group twin models, as well as graphical model output.

Install it from CRAN:


Most functions have extensive and practical examples (even figures for the twin models): so USE THE HELP :-).

See what is on offer with ‘?umx’. There are online tutorials at

umx stands for “user” OpenMx functions. It provides over 100 functions from high-level umxRAM and umxPath functions that make Structural Equation Modeling in R straightforward, to low-level functions to automate activities such as labeling, setting start values etc.,

Some highlights include:

  1. Building Path Models
  2. Reporting output
  3. Modify models
  4. Twin modeling!
  5. Easy-to-remember options
  6. Many more miscellaneous helpers e.g.

Feel free to use, and submit code and requests via Github. Tell your friends! Publish more good science :-)

For thrill-seekers and collaborators only: the bleeding-edge development version is here: