A Python package for Bayesian A/B Testing
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aByes is a Python package for Bayesian A/B Testing, which supports two main decision rules:

A lot of the underlying theory is discussed in this blog post.


  • In your target folder, clone the repository with the command:

    git clone https://github.com/cbellei/abyes.git
  • Then, inside the same folder (as always, it is advisable to use a virtual environment):

    pip install .
  • To check that the package has been installed, in the Python shell type:

    import abyes
  • If everything works correctly, the package will be imported without errors.


  • aByes is tested on Python 3.5 and depends on NumPy, Scipy, Matplotlib, Pymc3 (see requirements.txt for version


How to use aByes

The main steps to run the analysis of an A/B experiment are:

  • Aggregate the data for the "A" and "B" variations in a List of numpy arrays
  • Decide how to do the analysis. Options are: 1. analytic solution; 2. MCMC solution (using PyMC3); 3. compare the analytic and MCMC solutions
  • Set decision rule. Options are: 1. ROPE method; 2. Expected Loss method
  • Set parameter to use for the decision. Options are: 1. Lift (difference in means); 2. Effect size

These and many more examples and instructions can be found in this blogpost.


  • In IPython, type:

    import abyes as ab
    import numpy as np
    data = [np.random.binomial(1, 0.4, size=10000), np.random.binomial(1, 0.5, size=10000)]
    exp = ab.AbExp(method='analytic', decision_var = 'lift', rule='rope', rope=(-0.01,0.01), plot=True)
  • This will plot the posterior distribution:

  • It will then give the following result:

    *** abyes ***
    Method = analytic
    Decision Rule = rope
    Alpha = 0.95
    Rope = (-0.01, 0.01)
    Decision Variable = lift
    Result is conclusive: B variant is winner!
  • There are many more examples available in the file example.py, which can be run from the root directory with the command:

    python abyes/examples/examples.py


Currently, aByes:

  • only focuses on conversion rate experiments
  • allows for only two variants at a time to be tested

These shortcomings may be improved in future versions of aByes. (Feel free to fork the project and make these improvements yourself!)


Apache License, Version 2.0