Working papers

Simulating electoral system changes and how voters might respond
  • Article: Working paper [1.4M pdf]
  • Abstract: A crucial determinant of electoral system choice is how many seats a specific political party would win under some alternative electoral system. For decades this quantity has been estimated using a simple approach that is known to have multiple major flaws. I address these problems by developing a computational formal model that estimates how the seat totals in a particular single-member district plurality election might have been different if the election had been held under another electoral system, explicitly simulating how strategic voters might have voted differently. The model is falsifiable, and outperforms the widespread simple approach when applied to New Zealand’s electoral system change. I simulate recent Canadian and British elections under ranked-choice voting and proportional representation. The results suggest that several parties opposed election reforms that, when voters’ preferences are imputed from survey data and strategic voting is accounted for, could actually have benefited those parties.

  • How strategic are most voters? Evidence from simulations
  • Article: Working paper [457K pdf]
  • Abstract: Election results do not just represent peoples’ true preferences, but is that because most voters are slightly strategic, or because a few voters are highly strategic? This study examines the prevalence of four types of voters: sincere voters, partially strategic voters, precisely strategic voters, and those who vote based on party identification. A new method for comparing the results of a computational formal model to real election results suggests that many voters are slightly strategic, some voters are highly strategic, and a smaller number of voters are not strategic at all. A novel partially strategic heuristic is shown to be highly accurate, and models with only sincere voters actually produce less accurate results than models where every voter maximizes their utility. The results suggest that sincere voting, partially strategic voting, and precisely strategic voting were all prevalent in recent Canadian and British elections.

  • The probability of casting a pivotal vote in Instant Runoff Voting
  • Article: arXiv preprint
  • Abstract: I derive the probability that a vote cast in an Instant Runoff Voting election will change the election winner. I show that there can be two types of pivotal event: direct pivotality, in which a voter causes a candidate to win by ranking them, and indirect pivotality, in which a voter causes one candidate to win by ranking some other candidate. This suggests a reason that voters should be allowed to rank at most four candidates. I identify all pivotal events in terms of the ballots that a voter expects to be cast, and then I compute those probabilities in a common framework for voting games. I provide pseudocode, and work through an example of calculating pivotal probabilities. I then compare the probability of casting a pivotal vote in Instant Runoff Voting to single-vote plurality, and show that the incentives to vote strategically are similar in these two systems.

  • Election frauds or strategic voting?
  • Article: Working paper [871K pdf]
  • Coauthors: Walter Mebane and Fabricio Vasselai
  • Abstract: Election forensics identifies fraudulent activity from empirical distributions of election turnout and vote choice, but strategic behavior can affect these distributions in ways that might resemble fraud. Many types of election forensics interpret a multiplicity of modes in election data as indicators of frauds, but strategic behavior induces correlations among electors' behavior that can produce multimodalities. We design simulations to match equilibria derived in models of wasted vote logic and of strategic abstention, and we simulate elections in which we know that strategic behaviour is present while fraud is not. The results suggest that fraud detection models might misidentify legitimate strategic coordination as a signal of election fraud.

  • Iterative election games
  • Article: Working paper [594K pdf]
  • Abstract: In the period before a large democratic election, thousands of electors, with diverse preferences and very different ways of making decisions, update their ideas about which candidates are competitive and how they should vote. Iterative computer models allow us to study this process without abstracting away the notion of time, in a framework that avoids some of the less realistic assumptions of pencil-and-paper models. But how do we know when the model has converged to an election result? I demonstrate that certain broad categories of iterative election models produce cyclic behaviours in the electors' strategic intentions, and that those cycles obey simple rules. This opens up a new modeling framework that captures some of the dynamics of elections better than existing formal models can.