Shiro Kuriwaki (Yale Political Science), Jeff Lewis (UCLA Political Science), and Michael Morse (Penn Law) have posted this draft about whether releasing individual-level cast vote records would violate the secret ballot. Here is the abstract:

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.

Their working paper is featured in a new report by the Bipartisan Policy Center on the broader topic.