Click here for complete paper.
One thing we did in our experiment was to ask a number of user satisfaction questions as a followup. An important question in this batch was: "Are you confident that the machine correctly recorded your vote?" The majority of voters were very confident. Curiously, this confidence did not go down much when we rigged the machine to flip the votes for McCain and Obama.
Why? First, note that half the voters did not notice this switch (emphasis added). People felt strongly about their presidential preference, but people, in general, are not very good at proofreading. The summary screen that comes up at the end of the voting session clearly showed McCain for the Obama voters and visa versa, yet they did not notice.
Among people who did notice, the usual reaction was "Huh?" and then they went back to fix the problem. In general, people assume that the machine is right and assume that it was their error, not the machine's dishonesty. Only a small fraction of our voters
(or more properly, experimental subjects) commented on the fact that we'd flipped their votes.
This has important consequences for the real world. Most people do not complain when there is a problem. They assume that it was their mistake and go back and fix it. I assume that things would be different if the machine did not let them fix the vote flip, but if the machine lets them fix it, the fact that some voters are complaining suggests that there may be far more voters who notice the problem and are silent, and that even more voters may have had their votes flipped but didn't notice the problem.