A comment from a reader got me thinking about the difference between what people say in polls and what they do at the ballot box. So I decided to take a look.
For the 2006 and 2008 elections, I took the last poll from each of the active polling firms. In 2008 there were six who polled in the last few days (EKOS, Angus-Reid, Nanos, Harris-Decima, Strategic Counsel, and Ipsos-Reid). In 2006 there were four (Strategic Counsel, SES Research (now Nanos), Ipsos-Reid, and EKOS).
This chart shows the differences between the average polling result of these polling firms, and the actual vote totals each party received.It's difficult to draw conclusions from this with only two sets of data. The 2004 election doesn't seem to have been as frequently polled. Perhaps only after the next election will we be able to get a real picture of how parties do in polls vs. elections.
Let's take a look at the numbers. For the last days of 2008, the Conservatives averaged 34.5% in the polls. The Liberals were at 27.0%, the NDP at 19.3%, the Bloc at 9.7%, and the Greens at 8.8%. The actual election results were 37.7%, 26.3%, 18.2%, 10.0%, and 6.8%, respectively.
That means the pollsters under-estimated the Conservative vote total by 3.2 points and the Bloc's by 0.2 points. They over-estimated the vote totals of the Liberals by 0.7 points, the NDP by 1.1 points, and the Greens by 2 points.
But what does that really mean? Turnout was low, and the Liberals took the biggest hit in actual votes. If turnout had been what it had been in 2006, would the Conservatives have gotten the predicted 34.5%? It's impossible to say.
Looking at 2006, the Conservatives averaged 37.1% going into election day. The Liberals were at 27.8%, the NDP at 18.7%, the Bloc at 11.3%, and the Greens at 5.1%. Their actual vote totals were 36.3%, 30.2%, 17.5%, 10.5%, and 4.5%, respectively.
So this time the Conservatives were over-estimated by 1.2 points, as were the NDP (1.3 points), the Bloc (0.8 points), and the Greens (0.6 points). The Liberals were under-estimated this time, by 2.4 points.
As you can see, it is really impossible to say whether one party does better or worse in polls. Both the Liberals and the Conservatives saw relatively significant over- and under-estimations of their vote haul. Only the NDP, the Greens, and (to a lesser extent considering national totals for the Bloc are difficult to quantify) the Bloc were over-estimated in both election campaigns. The NDP's over-estimation is relatively high, at over an entire point in both elections. But the Greens were only 0.6 points higher in 2006, which is actually a pretty close estimate.
This really does show how the MOE is an effective way of safe-guarding polling results. We can reasonably assume that every pollster is within three-points at the national level. But with things being as close as they are, that is a huge margin. And for parties like the NDP, it can mean a historic best or a disastrous campaign.
The commenter in question was wondering if I should take this sort of "ballot box" effect into consideration when making my projections. Looking at these numbers, I don't think I can.
Have a great Thanksgiving weekend everyone! I'll post if a poll comes out during the weekend, but otherwise I'll see you Tuesday.