After an election, should election officials release an electronic record of
each ballot? The release of such cast vote records could bolster the legitimacy
of the certified result. But it may also facilitate vote revelation, where an
analyst unravels the secret ballot by uniquely linking vote choices on the
anonymous ballot to the voter's name and address in the public voter file. We
provide the first empirical study of the extent of vote revelation under
several possible election-reporting regimes, ranging from precinct-level
results to the individual ballot records known as cast vote records. Using
Maricopa County, Arizona, as a case study, we find that cast vote records could
reveal less than 0.2% of any voters' choices in the 2020 general election.
Perhaps counterintuitively, releasing cast vote records coded by precinct and
vote method are no more revelatory than releasing aggregate vote tallies for
each precinct and vote method. We conclude that cast vote records are
sufficiently privacy-protecting, and suggest how the privacy violations that do
remain could be reduced.Comment: Initial draft, 42 pages, 6 figures, 2 table