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Illustration by Anthony JenkinsThe Globe and Mail

When voters of Toronto-Danforth head to the polls to elect their next MP on Mar. 19, they will be choosing the candidate they feel best equipped to take the late Jack Layton's spot in the House of Commons. Emotions may run high in the riding but, whether by a resignation or a tragedy, voters have historically acted no differently in by-elections no matter what forced them to the ballot boxes.

Most by-elections are brought about by the resignation of a sitting member of Parliament, and often for happy reasons: the end of a long and successful career in politics, a nomination to the Senate or an ambassadorship, or an opportunity in the private sector that might allow an MP to spend more time with his or her family. Rare are by-elections forced by scandal, but they do occur. The death of a sitting MP, however, is a sad reason to head to the polls.

When Jack Layton passed away from cancer in August, he was the 38th MP to die in office over the past 50 years. While that might seem like an alarming statistic, it pales in comparison to the number of MPs who did not survive their time as an elected official earlier in Canada's history. Between 1867 and 1962, 279 MPs died in office – a rate of almost three MPs per year. Higher living standards, greater life expectancies, and the generally improving health of Canadians over time would seem to explain the great disparity between the country's first century and the last 50 years.

A by-election does not always occur after the death of an MP. In 12 of the 37 cases since 1962 that preceded Mr. Layton's passing, general elections were held before by-elections could be scheduled.

One might assume the passing of an MP would increase the chances of a party to retain the seat. In contrast to a resignation, when voters might be more willing to turn the page, the unexpected and untimely death of an MP would seemingly induce voters not to overturn the decision of the previous election.

A poll by Forum Research published last week by the Toronto Star would seem to confirm this assumption. It found that 61 per cent of voters in Toronto-Danforth intend to cast their ballot for Craig Scott, the NDP candidate. Only 19 per cent intend to vote for Liberal contender Grant Gordon, while 14 per cent plumped for the Conservative Andrew Keyes. That is virtually identical to the results of the May 2 election.

But while the assumption that the tragic passing of Mr. Layton makes the election of Mr. Scott more likely may be true in this case, history would give us no such indication.

In the 101 by-elections since 1962 that were caused by the resignation of a non-independent MP, the incumbent party has won 69 of them. In only 32 cases did the incumbent party lose. That is a retention rate of 68.3 per cent for the incumbent party.

There have been 25 by-elections in the last 50 years that were forced by the death of an MP. Two have taken place in the last 10 years. In 2005, the voters of Labrador elected Liberal Todd Russell to take the place of Lawrence O'Brien, the previous Liberal MP who died of cancer at the end of 2004. In 2006, Raymond Gravel was elected under the Bloc Québécois banner in Repentigny after the death of after bloquiste Benoît Sauvageau.

But overall, the incumbent party won in only 17 of these 25 cases, for a retention rate of 68 per cent. In other words, incumbent parties have been just as likely to win by-elections caused by resignation as they have been when they were caused by the death of an MP.

In Repentigny, Mr. Gravel increased the Bloc's vote share from the last election contested by Mr. Sauvageau. But in Labrador, Mr. Russell took a smaller share of the vote than did Mr. O'Brien in the 2004 general election. This appears to be par for the course, as in only about half of the 25 cases did the incumbent party increase their vote share. Based on this small sample, it would thus appear the cause of an MP's departure from the House of Commons plays little role in a by-election's outcome.

But that is a general statement – the popularity of Jack Layton and the national outpouring of grief after his death was exceptional. What motivates voters changes from election to election, and in this instance the memory of the late NDP leader will not be easily forgotten.

Éric Grenier writes about politics and polls at ThreeHundredEight.com

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