The Gallagher Index measures how well the makeup of a legislative body represents the proportion of votes cast to elect it. Some countries do this much better than others.
Hey hey, it’s election day here in New Zealand! By the end of the day we should know just who will be leading the country for the next three years. The electoral system here is a strange one: everyone votes twice, once for a local candidate and once for a political party. Whoever gets the most votes in each electorate gets into parliament, following the standard first-past-the-post “winner takes all” system. But our parliament gets topped up with extra candidates – each political party’s share of seats reflects their proportion of the overall national vote. In other words, if 55% of the voters choose a party, that party has 55% of the seats in parliament. It’s a pretty good system, because you rarely feel like your vote is a waste. Minor parties actually get a chance, and sometimes small centrist parties hold the balance of power – so politics leans towards compromise and cooperation (sometimes). Here’s an amazing earworm summary of the system:
New Zealand elections tend to be strongly proportional – the votes for parties and the proportion of those parties in parliament line up pretty closely. But how does that compare with other countries? Political scientist Michael Gallagher came up with an index that allows us to compare the proportionality of different elections, even when those elections are held under different systems. A low score (0-5) indicates a highly proportional election; a high score (10+) indicates the opposite. By this index, New Zealand does pretty well: it has bounced around 1 to 3 since adopting its current electoral system. Other countries with some form of proportional election do well by this measure: Germany, Denmark, Sweden, Brazil, Sri Lanka, Namibia…
The United Kingdom does not do so well. In the 2001 general election, for example, Labour received just over 40% of the votes but got more than 62% of the seats in parliament; the Conservatives won 31% of the votes but got only a quarter of the total parliamentary seats; the Liberal Democrats won 18% of the vote but had less than half that percentage in seats. Their Gallagher Index score? 17.76. Yeesh.
The United States is a funny one. The House of Representatives is pretty proportional, usually hovering around 6 or less. This is unsurprising because most people tend to vote for one of two parties, so it usually ends up quite proportional despite being mainly first-past-the-post. The presidential election uses that wacky electoral college, and the proportion of votes to electoral college representatives is often deeply skewed. Historically, that number has veered as high as 38 on the index (the 1984 election); for the last couple of presidential elections it has sat at around 10. I cannot find a good index of the proportionality of the US Senate – probably because it isn’t elected all at once but split into thirds. I assume that it’s bad because every state gets two senators, no matter how large or small the population. So a senator for Wyoming represents around 289,000 people, whereas a senator for Texas represents 14 and a half million. A disproportional blowout.
You can see the numbers for the Gallagher Index in the third link below, by the way. Just remember that this is a measure of voting proportionality; elections can be proportional and still be deeply flawed or unfair in other ways.