With a third of 2015 MPs not running, NDP turnover highest in at least 20 years

When the federal election campaign gets underway in earnest, parties will be missing dozens of incumbent MPs who have opted against running again — including 11 sitting NDP MPs.

The party is suffering the highest attrition rate of any with official status in the last six elections, going back to before the 2000 contest.

Combined with MPs the New Democrats have shed over the past four years, a total of 15 members elected in 2015 will not be carrying the orange banner into the 2019 race. That's more than one-third of the original caucus.

The attrition numbers include any MPs who were elected in one election but did not run for the party in the next. It does not include MPs who died in office, as it is meant to reflect changes in the caucus that are likely to have been politically motivated, from one direction of the other.

For the NDP, the rate encompasses 11 sitting MPs not running again, three who have resigned and one — Saskatchewan's Erin Weir — who was expelled from caucus.

In comparison, the Liberals have lost just more than 14 per cent of their class of 2015, which includes former ministers Jody Wilson-Raybould and Jane Philpott as well as sitting MPs like Andrew Leslie and Rodger Cuzner.

The Conservatives sit at a 23-per-cent attrition rate, with several longtime MPs like David Tilson, Kevin Sorenson and Rob Nicholson not running again. That's down from their own high in the past two decades, when more than 28 per cent of Conservative MPs did not run in the 2015 election.

The average attrition rate among all parties since 2000 has been 16 per cent.

In all, 68 MPs who were elected in 2015 for parties with official status have said they will not run for those groups (or have been barred from doing so) in 2019. Five of those MPs died in office, of which four are not included in the attrition rates calculated by The Canadian Press. Three were Conservatives and two were Liberals. Mark Warawa had announced he was not running prior to his cancer diagnosis, and is included in the rate.

Among the NDP MPs not re-offering are veterans like David Christopherson and Nathan Cullen, and the NDP's only Alberta MP, Linda Duncan. Since last year, MPs Kennedy Stewart and Sheila Malcolmson left for other jobs in politics in British Columbia, and former leader Tom Mulcair resigned his Quebec seat.

The NDP's attrition rate before the upcoming election is an outlier for the party. Its average across previous elections is the lowest of any party's at 14 per cent, and its rates have spiked only since its massive gains in 2011.

In an emailed statement, the party said: "There are probably as many reasons as there are individuals" for why MPs are not running again, expressing confidence in the candidates that have risen to fill the places of departing MPs.

Karl Belanger, a former national director of the party and an aide to former leaders Mulcair and Jack Layton, said many of the departures were unsurprising, as those veteran MPs needed to be persuaded to run again in 2015 as well, so some of the retirements were "a long time coming."

"Obviously, it is easier to convince people to run for you and run again for your party if you're high in the polls, which is not the case right now," he said.

Beyond the tough individual fights that could lie ahead, the apparently low chance of the party gaining power might play a role in the departures.

"Some of these veterans who have been around a long time in the same roles as opposition MPs were convinced that they perhaps had a shot at power, at becoming a cabinet minister," Belanger said.

"This doesn't seem to be in the cards at this stage."

Still, Belanger said the high turnover is an opportunity to bring fresh blood into the party and recruit star candidates in ridings that remain strong bets for the NDP.

One other reason incumbents might choose to call it quits is that they are tired of public life itself, said Chris Alcantara, a political science professor at Western University.

"Especially now with Twitter and social media, there's much more public scrutiny today than in previous years," Alcantara said. "People get tired of that and the stress on their families."

What effect the NDP's high attrition rate will have on that party in the coming election is unclear, as there is only a "weak" correlation between turnover and electoral prospects, Alcantara said.

Higher turnover means fewer incumbents, who do tend to have an advantage in Canadian politics. One study by researchers at Simon Fraser University and the University of British Columbia found incumbent MPs are roughly 10 per cent more likely to win their races.

Rookie candidates are also more likely to make mistakes, Alcantara said, or have less connection to their ridings than incumbents.

Generally, it's better for a party to retain its experienced MPs, but overarching themes like a "change" narrative and the overall popularity of the party are more important in determining their electoral fates, Alcantara cautioned.

That complicates the connection between attrition and election outcomes. And the two could be correlated, but not have any real causal effects on the other.

Still, over the past 20 years, nine caucuses have had attrition rates above the average and six of them lost seats in the following elections. Conversely, 13 have had below-average rates and just four of those lost seats.

Prior to the last election, Bloomberg News found just one instance in Canadian history when the attrition rate for a party exceeded the NDP's current figure: when over 40 per cent of Progressive Conservative MPs elected in 1988 did not run before their party's catastrophic defeat in 1993.