The Ali Zaidi Effect

Despite the lack of a firm party system in the Undergraduate Council, campaigns tend to be two-candidate affairs. Rarely does a third-party ticket do well, with 10% of the vote just about the upper bound. In fact, of the myriad third-party tickets over the past few years, only a couple have ever seriously threatened to effect the outcome of the election.

Still, the prospect of a third-party spoiler comes up in most close races, in large part because of the Council’s unique voting system. Under the Hare-Clark, or Single transferable vote, system, voters rank the candidates, and if the voter’s first choice has the least number of votes, then that candidate is eliminated and the voter’s vote goes to his or her next choice. The process is repeated until a candidate has collected a majority of the votes.

We can construct a scenario in which this redistribution of votes has a material effect on the outcome of the election. Let’s say we have a close race with two major candidates. We’ll call them Ben and Andrea. And let us further assume that there are, say, three other candidates, each of whom we can expect to garner between 50 and 200 votes. If Ben finishes with 10 more votes than Andrea, then the redistribution may very well alter the result. But if Andrea is up 350 at the end of the day, then she’s pretty much impossible to topple through STV.

We can get a little more specific than that, though. Here’s a table showing how each third-party candidate’s votes since 2002 have been redistributed:

First-place Second-place Percent Votes gained
Maats 2002 55 71 0.44 -16
Zaidi 2006 179 218 0.45 -39
Nicolais 2004 203 207 0.50 -4
Hwang 2006 118 110 0.52 8
Barro 2003 101 88 0.53 13
Voith 2005 228 189 0.55 39
Gillis 2006 29 22 0.57 7
Amadi 2006 70 52 0.57 18
Martel 2007 71 49 0.59 22
Smith 2002 279 113 0.71 166
Lurie 2002 37 14 0.73 23
Lurie 2003 64 23 0.74 41

Only three times have a candidate’s votes been redistributed in such a way that more votes went to the second-place votegetter than the first-place one. On the other hand, two of these three instances involved a significant number of votes, though the largest margin transferred — from Ali Zaidi’s 2006 run — gave Tom Hadfield only an additional 39 votes, far less than he would’ve needed to catch Ryan Petersen.

Even assuming the historically best distribution of votes (56% to the trailing candidate) and a relatively-high number of third-party ballots (500), it is statistically unlikely that a trailing candidate will ever receive more than 100 votes through redistribution. Unless and until an election with three or more equally-matched candidates occurs, the likelihood of vote redistribution changing the outcome is extremely small.

Comments (1) to “The Ali Zaidi Effect”

  1. I forgive you, Ali.