“The 2015 election will be the last election using first-past-the-post,” promised Justin Trudeau, Canada’s Prime Minister.

And there’s good motivation for his promise. Here at The Center for Election Science, we’ve consistently spoken out against first-past-the-post, also known as the choose-one plurality voting method. And proportional representation deserves to be a part of that conversation.

Canada has had multiple elections where a party has gotten the majority of the seats with a mere 40% of the vote. This peculiar outcome where the minority rules the majority is called a manufactured majority. And it’s very common for countries using first-past-the-post.

It’s this kind of oddity that’s caused Trudeau to push for proportional representation. So what is proportional representation? The Lego video demonstration in the video above gives a nice explanation, but it can also be described pretty simply. Proportional representation is a voting system that gives seats to parties or platforms in proportion to the number of votes that they receive. And it tends to avoid the manufactured majority problem that’s annoyed Trudeau and his party.

Canada has already attempted proportional representation at the province level. But so far that hasn’t worked out. The referenda that were attempted required a majority of 60%, and these referenda consistently fell short.

Trudeau has a couple options if he wants to push a proportional representation method. One is to propose a national referendum. The problem with this, however, is that it requires a very large majority—one that he’s unlikely to get. His other approach would be to implement a new voting system through parliament. His political opponents are fighting this route.

Either way he goes, he’s going to have to pick a voting method. And he’s got some options.

One option is to use a system called single transferable vote (STV). You can find the video on this conveniently located above here. STV is a ranking method used in multi-member constituencies. It’s important not to get this mixed up with instant runoff voting or ranked choice voting. Those are reserved just for single-winner constituencies, which prohibit any level of proportionality.

The way STV works is by identifying a threshold of support among first-choice rankings. Candidates meeting this threshold get elected. It also preserves the voting power for voters that prioritize eliminated candidates and for voters that elected a candidate with votes surpassing the required threshold. STV can demonstrate some quirky behavior but it’s nowhere near as bad as the atrocious behavior first-past-the-post demonstrates within a winner-take-all system.

Another perk of single transferable vote is that you preserve some geographic representation—particularly if it’s used for five-seat districts. Of course, this geographic representation is not as tight as you’d find in a single-member district. Unfortunately, STV sacrifices some of its proportionality to achieve this geographic representation.

Party list proportional representation is another option. Party list—unlike STV—doesn’t preserve geography. But what it does do is provide an even more proportional outcome. And it does that by treating the entire nation as a single district.

The way party list works is that a voter chooses a party and then chooses a candidate within that party’s list. This is for an open system. If it’s using a closed list then the voter doesn’t get to choose the candidate. The system also accommodates independent candidates by treating independents as a sort of party. But this only works with an open party list system.

Another voting option for Trudeau is mixed member proportional representation. As you can see, his colleague Craig Scott is a fan. This approach gives a bit of a compromise between proportionality and geographic representation. It accomplishes that by having the nation as a single large district just like a party list system. But in addition, voters also elect local representatives in single-winner elections. Having local representatives upends some proportionality, but the system fixes that by having extra seats designated specifically to regain that balance.

Of course, we would offer a reminder that for single-winner districts there are better options than first-past-the-post. Obviously, approval voting would be a fine choice for any single winner election.

It’s worth noting that if Trudeau only switches out first-past-the-post for an alternative single-winner method, it’s not going to address the false majority issue. You need a proportional method to do that. If he pushed something like ranked choice voting, for instance, this reform wouldn’t accomplish the goal of proportional representation. No single-winner method can do that.

There are some other proportional options too, particularly within districts that hold 5 to 10 seats. You can actually adapt approval voting or score voting systems to be proportional in this type of context. For those new to these methods, approval voting lets you choose as many candidates as you want and score voting lets you score each candidate on the scale. These methods are typically used for single-winner elections.

Approval and score voting can be adapted into proportional methods by reweighting voters’ ballots whenever blocs of voters elect someone. This gives an opportunity for other voters who haven’t elected anyone to have a say. This idea is also how STV works. But with approval and score voting it can provide a more appealing first-round winner. Plus, using approval and score based methods can avoid some anomalies.

Whatever Trudeau decides to go with, commentators have suggested that he’s going to have to get moving soon. Creating and implementing the logistics of a new voting system is not something you can put off to the last minute.