With the upcoming French presidential election first-round contest looking more and more like a four-way race, now is a good time to visualize performance of candidates across the two rounds of majority-runoff presidential elections.
The data plot here graphs the top two candidates’ shares of the vote in the first round (y-axis) against their runoff share (x-axis). The candidate who had the most votes in the first round is shown with a circle, and the second candidate with a triangle. This is from the Shugart-Taagepera dataset, which contains 117 presidential elections in countries with politically significant presidents. There are 34 elections depicted in the graph–all those in which the rule was that a candidate needed over 50% to win in the first round, but no candidate achieved that threshold.
The solid line at 0.5 marks the runoff victory threshold, thus allowing us to see at a glance how close the runoff was.
Two noteworthy facts:
- A leading candidate under 25% is unusual. In this dataset, there are only two prior such cases–both in France (1997 and 2002).
- When no one can crack about 35% the votes, it becomes quite likely that the runoff will be won by the second-place candidate. (That is, after all, why there is a runoff; the first-round leader might not be a consensus pick.) The graph shows nine cases in which the first-placed candidate initially had under 35%, and in six of those the trailing candidate came back to win the runoff. Three of these winners started out under 30%.
Many polls suggest that France could wind up in both these categories in 2017.
A final curious observation: The dashed diagonal line marks equality of second and first round shares. One might think that no candidates would be to the “northwest” of this line, as in a two-candidate runoff, both candidates might be expected to increase their vote share following a first round that had three or more competitors. Yet two runoff contenders managed to lose vote share between rounds. The dubious distinction goes to John Atta Mills in Ghana in 2000 (44.5% in the first round, 43.1% in the runoff) and Geraldo Alckmin in Brazil in 2006 (41.6%, then 39.2%). In both cases, turnout may have been a factor; the number of votes cast was lower in both runoffs than it had been at the first round. Jean-Marie Le Pen was close to this line in the French 2002 election, but he did manage a small increase in his vote share, even with a large increase in turnout in the runoff following the shock of the National Front showing in the first round.