Clearing up confusion: why we can compute the probability of a decisive vote, even though the election might be decided by a recount
October 30th, 2008, by Andrew
Regarding the probability-of-a-decisive-vote calculation, I’ve received several comments along these lines:
Given the virtual certainty that there would be a recount in a decisive state where the election was very close (not to mention decided by a single vote), and given the virtual certainly that the recount would not yield a second identical result, wouldn’t the true probability that one’s vote would make a difference in both the original count and the recount be many times larger than your estimates? I’m not sure how to calculate that higher probability — but I suspect it would range between 2 X and X-squared where X is the Gelman probability that your vote would be decisive.
My reply: No, that’s not right. See footnote 6 of the article, which points you to p.674 of my BJPS paper with Katz and Bafumi which addresses this issue. The key is that, at some point, the election is determined, and each vote slightly changes the probability of McCain or Obama is winning. Before the election, the exact vote margin is uncertain, and the probability that your vote is decisive must be calculated by averaging over all possible vote margins that might occur. The result is that our calculation works out.
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Entry Filed under: Voting
3 Comments
Add your own1. What is the probability y&hellip | October 31st, 2008 at 1:22 pm
[...] See here for more discussion of why we can compute the probability of a decisive vote, even though the election might be decided [...]
2. Abe | October 31st, 2008 at 3:26 pm
Thanks for clearing this up, it addressed my prior question exactly.
3. Jeff | December 3rd, 2008 at 8:01 pm
I understand your point and reasoning behind a recount scenario, but who has the voting power in a recount? The original voters or the recount officials/judges?
Many Democrats argue that the Supreme Court decided Florida in ‘00. And that vote came down to hundreds (or was it thousands).
Determining what constitutes a vote seems to be more relevant in a tight recount than my trek down to the polling station. In every recount I have heard of votes disappear or magically appear. The decision always goes to the courts and lawyers. Washington state had a pretty notorious election in ‘00 (I recall).
I don’t think it is possible for any election at the state level to be decided by one normal citizen’s vote.
PS- voting need not involve driving at all…
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