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With each election comes the promise of change. Voters can throw a government out, install a new one, or give those in power a new mandate to tackle the issues the country faces. Millions of dollars are spent, names are dragged through the mud, and, in the end, about four out of every five people we elected last time are sent back to Ottawa again.

Incumbency is one of the most powerful forces in politics. According to a study conducted for The Hill Times last spring, 78 per cent of incumbents standing for election have been re-elected in Canada since 1968. In the last two elections, that number was inflated to 87 per cent. The odds of beating an incumbent are slim.

But an analysis of a random sample of almost 200 ridings indicates that sophomore MPs are no easier to beat than veteran MPs who have been around for 15 years or more.

According to this analysis, over the last two elections there has been no statistically significant difference between the re-election rate of an incumbent first elected in 2004 or 2006 and an incumbent whose political history stretches back to 1993 or earlier.

In 2006 and 2008, first-time incumbents were re-elected about 88 per cent of the time, no different than incumbents who were running in their fourth or fifth election. Incumbents who already had five or more electoral victories under their belts were re-elected about 91 per cent of the time.

That a long-time MP has just as much of a chance of being defeated as a newcomer would come as no surprise to former MPs Rahim Jaffer, Reg Alcock, Denis Paradis, Anne McLellan, or Ethel Blondin-Andrew, the first aboriginal woman elected to the House of Commons. They all met defeat after being elected four or more times previously.

But the stability of incumbency does not transfer over to their parties when MPs choose not to run again. In the last two elections, the incumbent party only won about 65 per cent of the ridings in which there was no individual incumbent. While the incumbent party still holds the edge, the advantage is nowhere near as great as when a sitting MP stands for re-election.

This is born out by the average change in vote share when there is no incumbent. In 2006 and 2008, vote shares changed for incumbents from one election to the next by an average of only 0.03 points. By contrast, vote shares dropped by an average of eight points for the incumbent party when a new candidate stood to replace a departing MP.

But incumbency does not ensure stability. With the help of Danny Williams's opposition to the federal Conservatives, Liberal incumbents Scott Simms, Gerry Byrne, and Todd Russell in Newfoundland and Labrador had their vote increase by an average 17.8 points between 2006 and 2008. On the other side of the coin, Bloc MPs in the Quebec City region saw their vote drop by as much as 16 points in 2006 when the Conservatives made their breakthrough in the provincial capital.

In addition to dropping, the vote also tends to swing more wildly without an incumbent. The average change in an incumbent's vote in 2006 and 2008 was approximately +/- 5.04 points, while the vote for the incumbent party in ridings without an incumbent MP varied by an average of +/- 9.51 points.

Stephen Harper performed the difficult feat of unseating an incumbent in 1993, when the Reform Party swept the Progressive Conservatives from western Canada. After deciding not to run again in 1997, Rob Anders took his place and kept the seat for the Reform Party but lost five points in the process. Since Mr. Harper's return as an MP for Calgary Southwest in 2002, he has maintained his share of the vote between 68 and 72 per cent in the riding, amply demonstrating the stability of the incumbent.

Michael Ignatieff, on the other hand, took on the role of a new candidate after the retirement of Liberal MP Jean Augustine. In his first campaign in 2006, he lost about seven points for the party in Etobicoke-Lakeshore, an example of the challenges a new candidate faces. But in 2008, as an incumbent for the first time, he increased his party's vote by about three points, and joined 240 other incumbents re-elected that year.

Éric Grenier writes about politics and polls at ThreeHundredEight.com

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