Jeremy Corbyn speaks on stage after he is announced as the new leader of  the Labour Party during the Labour Party Leadership Conference in London, Saturday, Sept. 12, 2015. Corbyn will now lead Britain’s main opposition party. (AP Photo/Kirsty Wigglesworth)

Jeremy Corbyn, a parliamentarian on the far left, won the leadership of the British Labour party in a disputed election that involved hundreds of thousands of new registrants under newly adopted party rules in which “any voter could sign up as a registered member and cast a vote for just £3.”

What are the stakes? As party leader, Corbyn is the presumptive Labour candidate for prime minister in the next U.K. general election, scheduled for 2020. And Corbyn is viewed negatively from the center-right of his party. Former prime minister Tony Blair said last month that “Labour is in ‘mortal danger’ and faces ‘annihilation’ if Jeremy Corbyn is elected leader.” And, after the recent vote, Rob Marchant, a former Labour party manager from the Tony Blair era, wrote in the London Independent that “today is our darkest hour – we have become unelectable,” comparing Corbyn’s chances unfavorably to those of Michael Foot, the Labor leader who was destroyed by Margaret Thatcher in 1983.

What does the political science tell us? I will say right away that I am much more familiar with the U.S. literature on elections. I will translate what I know as well as I can, inserting qualifiers as necessary.

Corbyn’s critics offer two strikes against his electability. First is the disputed nature of his leadership election, which implies that his support within the party is not as strong as it might sound from the numbers of his decisive victory. Second is his stance on the political margins, far to the left of the median U.K. voter.

I can’t really comment on the disputed-election thing. I can only assume it will hurt Corbyn. On the other hand I’d guess the effects would be relatively short-term; that is, if Corbyn remains as Labour leader all the way until 2020, the circumstances of his ascension shouldn’t be so important.

What about the ideological extremism of Corbyn and his supporters? In the U.S. there’s evidence from various sources that candidates on the far left and far right do not do so well, electorally speaking, compared to more moderate candidates. This is consistent with the so-called median voter theorem which suggests (under simplified conditions) that parties are most likely to win elections if they run candidates near the ideological center. But this “theorem” is only an approximation. In real life, ideologically extreme candidates such as Ted Cruz, Bernie Sanders, and Ronald Reagan do get elected to high office. (Yes, Cruz was elected in Texas and Sanders in Vermont, but Cruz’s positions are far to the right of the median Texan’s and Sanders is to the left of the median Vermont voter.)

Jonathan Katz and I have writtenGeorge of “the moderate benefits of moderation” in politics: in U.S. congressional elections we estimated that ideologically extreme candidates of either party can do up to 5 percentage points worse, compared to moderates:

median.png

Here is a recent paper I found on the web by Henry Kim and Brad LeVeck, “The Declining Value of Moderation in US House Elections,” which is consistent with the above graph.

And in his classic book from 1983 political scientist Steven Rosenstone estimated that ideological extremism cost some presidential candidates up to 2 percentage points of the vote.

That is, Barry Goldwater got destroyed in 1964 and George McGovern likewise in 1972 [in earlier version of this post I used Walter Mondale in 1984 here, but McGovern is a better example of someone on the ideological edge of his party], but our best estimate is that more moderate candidates still would’ve lost, just not by quite as much. And a more moderate alternative to Ronald Reagan would likely have won an even larger landslide over Jimmy Carter in 1980.

Journalists like to tell candidate-specific stories, but all the research I’ve seen shows that that candidate-specific effects happen on the margins. Thus, for example, I emphatically disagreed with Matt Bai’s claim that Gary Hart was “close to a lock” for the presidency had he been nominated in 1988.

But back to Corbyn. Based on the analogy to U.S. presidential elections, I’d dock 2 percentage points from Corbyn’s vote for his position on the left edge of his country’s politics. But this doesn’t tell the whole story. Besides the obvious difficulty of extrapolating from one country to another, there also is the U.K.’s multiparty system. In recent decades, and in 1983 in particular, Britain has had a center party (now the Liberal Democrats) that can take the votes of disaffected Labour supporters. On the other side, Labour competes with the nationalist party in Scotland. Any analysis of the British political scene needs to account for these factors, along with the aforementioned concern of the strong opposition to Corbyn within his own party.

But just considering the challenges of running a far-left candidate supported by one of the two major parties, I’d guess the Labour party is costing itself a few percentage points of the vote. Which, depending on economic and political conditions in four years, could lose them the election, or not.