Voting Systems in Canada: Mixed Member Proportional

Result of Ontario’s referendum on Mixed Member Proportional

A common form of proportional representation used around the world is one called Mixed Member Proportional. This system involves electing two different types of representative to the relevant legislature: local constituency representatives, who are usually elected by plurality vote, and list representatives, who are allocated to the parties based on the share of the vote. The aim is that the share of representatives mirrors the share of the popular vote.

Result of the 2011 Welsh Assembly election, which uses MMP
Result across Wales’s 40 assembly constituencies

In such a system, the tricky bit is figuring out how many seats to be for constituencies and how many for list seats: too few constituency seats, and the local representation is very weak; too many constituency seats, and you lose the proportionality. The Welsh Assembly is a prime example of what happens if this ratio is wrong: under pure PR, the Labour party would only be entitled to 22 out of 60 seats, as but the party already won in 28 constituencies, they are already guaranteed to have at least a handful of what are called overhang seats. Further, as Wales’s list seats are based on region, Labour gets additional seats in a region where they didn’t do as well, which leads them to have half the seats with only 37% of the party vote.

In most countries, the list seats are allocated proportionally by region of the country. For this purpose, I’m going to borrow the regions used for the purposes of the Senate: Maritimes, Québec, Ontario and Western. In each of these regions, I will keep the number of seats the same as they have presently, and keep the ratio of constituency to list MPs as close to equal between them as mathematically possible. As before, each territory will get one seat.

How the Canadian House of Commons would look with varying degrees of constituency/list seat splits

If we keep the fraction of constituency seats below 60%, we find that proportionality is maintained across all four regions. Once we surpass this, though, the Liberals the Liberals start to gradually pick up overhang seats at the expense of other parties. If this fraction increases to 80%, it would be enough for the Liberals to keep a majority government. It’s worth noting that the Ontario referendum in 2007 was for 70% of seats to be for constituencies, and this will have been high enough for Dalton McGuinty’s provincial Liberal party to gain a handful of overhangs (though not enough for a majority).

If Canada elects for this system, it would be easiest to split constituency and list seats 50:50, similar to what is done in Germany. This allows for strong local representation to be maintained while still keeping the intended proportionality.

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