After a quick look at
competitiveness last week, I wanted to touch on incumbency effects today.
First of all, the technical part - if this bores you, just scroll down to the
bolded line below. I won't think any less of you.
To see how important an incumbent is, we need a way to calculate an
expected result. After spending a lot of time tinkering with various projection models, I've come to the
conclusion that a simple arithmetic transfer of votes works the best - at least for the 2006 and 2008 election, which is what I'm looking at (if you want to see residual charts and regressions and such to prove this, just e-mail me). So I carved the country into 30 geographic regions and projected accordingly - if the Liberal vote dropped 2 points in Calgary last election (it did!), I subtracted 2% from the 2006 result from every Calgary riding.
How accurate is this? Well, half the results fall within +/- 2% of the actual result, with 90% falling within +/- 6%. The predicted values correlate 96.3% with the results. Keep in mind, we don't expect the results to be spot on because, after all, the candidates and campaigns
should make a difference.
For those interested in the fine print, by election winners were considered to be incumbents, so Bob Rae was an incumbent MP last election. And Garth Turner became a Liberal incumbent, with
Wajid Khan as a Tory incumbent (for what it's worth, Turner's impact was negligible, while Khan, not unsurprisingly,
undershot the expected Tory vote by 3%).
So what does the data show?
For both 2006 and 2008, in ridings without an incumbent, the incumbent party took a 4.1% hit compared to their expected result. Since the totals have to sum to zero, that means incumbents performed about 1% above expected, for an overall benefit of around 5%. These results were largely identical both elections and mesh well with the academic literature on the subject so I don't have any reason to doubt them.
What's also interesting, as an aside, is that
MPs were more likely to call in quits in regions where their party was heading for a drop in support (think of the Tory Newfoundland
MPs before last election). So "
spending more time with my family" loosely translates to "
I can see the writing on the wall" quite often.
Now, I do think it's important not to read too much "cause and effect" into this. As Andrew Steele comments
here (citing
freakonomics...a book I
adore), incumbency effects are often overblown once other factors are controlled for. And when we're talking about "incumbency", we're really talking about resources, organization, and "name recognition" - Gerard Kennedy and Justin Trudeau weren't incumbents last election but I'd wager a lot more people knew who they were in their home
ridings than many obscure backbenchers (I'm looking at you Brian Jean). Quite simply, not all incumbents are created equal. But a 5% swing is nothing to sneeze at - 41
MPs were elected by smaller margins than that last time.
So, once
MPs start announcing their retirement, we should be paying attention. Because if they're running in
ridings with a slim margin of victory, it certainly could put those seats into play.
Labels: Brian Jean, fun with numbers, incumbency advantage
