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update numbers in the paper to reflect notebooks
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kellieotto committed Jan 21, 2019
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Expand Up @@ -397,7 +397,7 @@ \section{Numerical examples}\label{sec:examples}
Jupyter notebooks containing calculations for hybrid stratified audits intended to be relevant for Colorado are available at \url{https://www.github.com/pbstark/CORLA18}.
\texttt{hybrid-audit-example-1} contains two hypothetical examples.
\texttt{hybrid-audit-example-1} contains two hypothetical elections.
The first has $110,000$ cast ballots, of which
9.1\% were in no-CVR counties.
The \emph{diluted margin} (the margin in votes, divided by the total number of ballots cast) is $1.8\%$.
Expand All @@ -412,12 +412,12 @@ \section{Numerical examples}\label{sec:examples}
A ballot-polling audit of the entire contest would have been expected to examine about 14,000 ballots, more than 10\% of ballots cast.
The hybrid audit is less efficient than a ballot-level comparison audit, but far more efficient than a ballot-polling audit.
The second contest has 2~million cast ballots, of which 5\% were cast in no-CVR counties.
The second hypothetical election has 2~million cast ballots, of which 5\% were cast in no-CVR counties.
The diluted margin is about $20\%$.
The workload for SUITE at 5\% risk is quite low:
In 100\% of 10,000 simulations in which
the reported results were correct, auditing 43~ballots from the
CVR stratum and 15~ballots from the no-CVR stratum
In 93\% of 10,000 simulations in which
the reported results were correct, auditing 50~ballots from the
CVR stratum and 25~ballots from the no-CVR stratum
would have confirmed the outcome.
If it were possible to conduct a ballot-level comparison audit for the entire contest,
an RLA at risk limit 5\% could terminate after examining 31~ballots if it found no errors.
Expand All @@ -428,15 +428,16 @@ \section{Numerical examples}\label{sec:examples}
The reported margin is just over $1\%$, but the reported winner
and reported loser are actually tied in both strata.
The risk limit is 5\%.
For a sample of 500~ballots from the CVR stratum and 1000~ballots from the no-CVR stratum,
the maximum combined $P$-value is over 25\%, so the audit cannot stop there.
For a sample of 7600~ballots from the CVR stratum and 400~ballots from the no-CVR stratum,
the maximum combined $P$-value is 1, so the audit cannot stop there.
A third notebook, \texttt{fisher\_combined\_pvalue}, illustrates the numerical methods used
to check whether the maximum combined $P$-value is below the risk limit.
It includes code for the tests in the two strata,
for the lower and upper bounds $\lambda_-$ and $\lambda_+$ for $\lambda$,
for evaluating Fisher's combining function on a grid,
and for computing bounds on the $P$-value via Equation~\ref{eq:lowerbound}.
and for maximizing the $P$-value, using the local modulus of continuity
for Equation~\ref{eq:fisher-hybrid} to bound any approximation error.
\section{Discussion} \label{sec:discussion}
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