Of the electoral reform proposals on offer, the one I’m most in favour of is the preferential or ranked ballot, also known as the alternative vote, where voters mark their first, second and third (and so on) choices (rather than simply an X). If no candidate wins 50 percent on the first round, the candidate finishing last is dropped and their voters’ second preferences are redistributed, and then the next candidate, and so on and so on until someone gets 50 percent.

It’s a bit more complicated than marking an X, and counting (and calculating!) the votes will almost certainly take longer, but a preferential ballot has a couple of things going for it. For one, it ensures that any member of Parliament will eventually be elected by 50 percent of the vote, once second- and third-place preferences are redistributed—we won’t have close three- or four-way races where the winner ends up with only a handful of votes more than the others, and less than 40 percent support.

For another, it’ll make strategic voting obsolete. No longer will I have to wonder whether voting for candidate X instead of candidate Y will allow the foul candidate Z to get elected: I can simply rank candidates X and Y on the ballot and leave candidate Z off the ballot altogether. (I have strong objections to strategic voting: in practice it’s been weaponized to get other parties’ supporters to support your candidate, and parties haven’t always been honest about who’s ahead and who’s behind when doing it.)

But changing the rules does benefit some players more than others. This is true of any change, including proportional representation, which is one reason I suspect electoral reform has been so elusive: the sense that the rules are being tweaked for someone else’s benefit.

In the case of the preferential ballot, that someone else is largely expected to be the Liberals, because as the centrist party they’re most likely to get second-preference votes from both the right and the left. No surprise, then, that a preferential ballot is reportedly the Liberals’ preferred option.

It’s one thing to expect something, quite another to quantify it. What would the 2015 election results have looked like with a preferential ballot? Two separate models have tried to answer that question, each using slightly different methodologies: Éric Grenier of ThreeHundredEight.com and University of Lethbridge political scientists Harold Jansen and Peter McCormick. The following table shows the results of their models, along with the actual 2015 results and what the results might have been under proportional representation:

Party 2015 Results Grenier Jansen/McCormick Proportional
Liberal 184 224 205 134
Conservative 99 61 73 109
NDP 44 50 52 67
BQ 10 2 7 16
Green 1 1 1 12
Preferential Ballot Models, 2015 Canadian Federal Election Results

While necessarily inexact—the models apply regional polling data on voters’ second preferences to individual riding results, and the impact of strategic voting, which would be different under a preferential ballot, is impossible to quantify—it can fairly be said that a preferential ballot would largely benefit the Liberals (and to a lesser extent the NDP), at the expense of the Bloc Québécois and the Conservatives.

A preferential ballot benefits both the Liberals and the NDP because many of each party’s supporters will opt for the other one in the next round. And it punishes the Conservatives—but mostly because they’ve alienated just about everyone except their core supporters. Polls have repeatedly shown that few Liberal and NDP voters have the Conservatives as their second choice, and many Conservative voters say they don’t have a second choice.

That might change under a preferential ballot. Grenier argues that parties would change the way they campaign under a preferential ballot—they’d have to: “Energizing the base and taking swing voters away from other parties would no longer be enough—leaders would also need to woo supporters of their opponents for those second-choice votes, and avoid alienating other voters entirely.” So the Conservatives would have every incentive to be nicer to people outside their narrowly identified base. And so would every other party. Because if they didn’t, they would lose every close riding once the second and third preferences were redistributed.

It would not change the system very much at a macro level: Jansen and McCormick calculate that only 32 seats would change hands, and the system’s tendency towards majority governments would be even stronger. But at a more granular level some of the more toxic tendencies of our present system—narrow wins with a split electorate, strategic voting, riling up the base instead of appealing to the broad electorate—might be addressed.