# Bayesian Methods for Post-Election Audits

This page provides additional support and information related to the paper:

``A Bayesian Method For Auditing Elections''

by Ronald L. Rivest and Emily Shen

in *Proceedings of EVT/WOTE 2012*

The slides for the conference talk are here.

## Code

#### Related work

Philip Stark has provided some excellent tools
for risk-limiting post-election audits at:

Tools
for Comparison Risk-Limiting Election Audits

In particular,
his page provide strong support for randomly sampling the cast ballots
in random order for a single-ballot audit. This capability may be
useful in conjunction with the tools provided here, for doing Bayesian
audits.
#### Javascript

We have implemented the basic Bayes ballot-polling audit
here.

This page implements an N-type audit: it uses a single prior, where all ballot
types are equally likely and where all possible tallies are equally
likely.

The implementation uses the Dirichlet approximation to the Polya
method; this may be inaccurate if the difference between the number
of cast ballots and the size of the audit sample is very small.

If a candidate has a winning probability in excess of 95%, the
corresponding bar on the ``winning probabilities graph'' turns red.
If this candidate is also the reported winner of the contest, then
the audit may reasonably stop at this point.

#### Python

We have also implemented the Bayes audit method in Python; contact
the authors to obtain copies of this code.

Ronald L. Rivest `rivest@mit.edu`

Emily Shen `eshen@csail.mit.edu`