Electoral Reboot: Gallagher Index

Electoral Reboot: Gallagher Index

December 1, 2016 2:32pmET

The Special Committee on Electoral Reform supports using the Gallagher Index to determine an acceptable proportional system as an alternative to Canada’s current First Past the Post system.

What is the Gallagher Index?

Developed by Irish political scientist Michael Gallagher (a committee witness during the summer), this formula measures the difference between a party’s overall popular vote and the seats they hold in a legislature. The goal is to determine how proportionate (or disproportionate) the legislature’s party standings are compared to the overall vote.

An index number under five per cent is deemed excellent, according to testimony. The committee recommended this as a goal for any new electoral system.

Byron Weber Becker, a University of Waterloo lecturer, calculated the 2015 federal election at 12 per cent. Alternative Vote in 2015 would have raised the number to 15 per cent, while MMP would produce an index score of nine percent.

(The mathematical formula goes like this. The difference between the vote percentage and seat percentage for each party are squared and added together. That total is divided by two. The square root of that number is the result.)

The Liberal supplemental report expresses doubt that the Gallagher Index’s usefulness has been established – saying a score below five would require radical changes to the House of Commons.

Watch Gallagher’s committee testimony from July 28, 2016:

-Andrew Thomson