What is the Gallagher Index?
The Gallagher Index measures how unfair a voting system is.
It looks at how we voted.
It looks at how we're represented.
Then it says how different those two are.
A high Gallagher index means that parliament doesn't reflect how people voted.
How is it calculated?
| Votes | Seats | Vote % | Seat % | DifferenceDiff | Squared | |
|---|---|---|---|---|---|---|
| {{ party.Shortname.replace(/\./g, "") }} | ||||||
| Sum | ||||||
| Halved | ||||||
| Square rooted | ||||||
Resulting Gallagher Index
— {{ Math.round(gallagherIndex) }}% —
So now when someone shows you this formula
you know it's just a way to calculate average fairness.
2016's discussion of the Gallagher Index
In December 2016, Canada's 2016 Special Committee On Electoral Reform made the following recommendation to parliament:
The Committee recommends that the Government should, as it develops a new electoral system, use the Gallagher index in order to minimize the level of distortion between the popular will of the electorate and the resultant seat allocations in Parliament. The government should seek to design a system that achieves a Gallagher score of 5 or less.
| Gallagher Index | Voting system |
|---|---|
| Alternative Vote | 19.0% |
| First-Past-The-Post | 12.0% |
| AV+ | 13.4% |
| Mixed Member Proportional (Lite) | 9.0% |
| Mixed Member Proportional (Small Regions) | 3.8% |
| Rural-Urban PR (More Singles, 389 Seats) | 1.9% |
| Rural-Urban PR (Few Singles) | 2.4% |
| Riding Centric Rural-Urban PR | 1.5% |
| Rural-Urban PR (More Singles, 338 Seats) | 2.7% |
| Single Transferable Vote (Medium-sized Regions) | 3.3% |
| Single Transferable Vote (Small Regions) | 5.6% |