Shares are of valid votes: votes for a candidate, including write-ins and, in Nevada, “None of these candidates,” which is a choice on the ballot. Ballots recorded as blank, over-voted (more than one candidate marked), under-voted or void are not votes for anyone, and are left out. So are blank and spoiled ballots in states that don’t report them at all.
In a few places, the certified returns combine categories. In Massachusetts and New York in 2008 and 2012, some write-in votes are recorded together with blank ballots and can’t be separated. We treat these combined rows as invalid, because blank ballots are the dominant part. These combined rows account for a very small percentage of each state’s total vote: Massachusetts (0.71 percent in 2008, 0.52 percent in 2012); New York (1.10 percent in 2008, 0.90 percent in 2012).
In Vermont in 2024, 268 rejected ballots are recorded among the votes. And in 2008, 12,490 third-party votes in Rhode Island and the District of Columbia are left out, because no survey respondent there reported such a vote.
None of these cases result in any material difference in what we report.