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formulae is a Python library that implements Wilkinson’s formulas for mixed-effects models.

This package has been written to make it easier to specify models with group effects in Bambi, a package that makes it easy to work with Bayesian GLMMs in Python, but it could be used independently as a backend for another library. The approach in this library is to extend classical statistical formulas in a similar way than in R package lme4.


formulae requires a working Python interpreter (3.7+) and the libraries NumPy, SciPy and pandas with versions specified in the (see requirements.txt for version information).


The latest release of formulae can be installed using pip:

pip install formulae

Alternatively, if you want the development version of the package you can install from GitHub:

pip install git+


See the GitHub contributor page.