@unpublished{Riv20a, author = { Ronald L. Rivest }, title = { {Double-Bubble Ballots} }, date = { 2020-01-09 }, OPTyear = { 2020 }, OPTmonth = { January 9, }, abstract = { We propose and discuss a format for optical-scan ballots where each selection has {\em two} bubbles. This format may be used for both machine-marked (e.g. by a BMD) and hand-marked ballots. The first column of bubbles is called the {\sc Vote} column; this may be marked by the machine. The second column is the {\sc Lock} column; this may be used by the voter to confirm (or override) the vote in the {\sc Vote} column. \par Normally a voter would fill in the {\sc Lock} column with the same selections as shown in the {\sc Vote} column, confirming that these selections are indeed what the voter intends. \par However, the double-bubble format has the advantage of allowing a voter to change their mind (spoil a ballot) without necessitating a new ballot; as the {\sc Lock} column may act as a fresh ballot. \par Voters are motivated to complete the {\sc Lock} column by hand, as it prevents a third party from changing their vote later (as would be possible if the {\sc Lock} column were left blank). \par This explicit indication of verification by the voter of their choices may mitigate some of the problems seen with BMD (ballot-marking devices), where voters are observed to frequently not verify their ballots. \par The double-bubble proposals is designed to motivate voters to verify their BMD-printed ballots. It does not address the problem that voters may have limited recall of the choices and may thus have cognitive limitations on their ability to verify the ballot. See (DeMillo, 2018) for more discussion of this point. } }