Thursday, March 14, 2013

Something old, something new: the Conservative slide in the polls

In this week's piece for The Globe and Mail, I take a closer look at the polling trends. They are certainly negative for the Conservatives, but as I show in my article it is nothing they haven't seen before. Sort of - while the mid-mandate slide is something they experienced after the 2006 and 2008 elections, this one might be the worst yet.

I love scatter plot charts as they are probably the best way to represent just how noisy the data can be in polls. But they also show how (to borrow from Nate Silver), there is often a signal in the noise.

A simple linear trend line gives one indication of where each party's support is headed, but it is worthwhile to look at where they are meandering as well. The chart above shows support at the national level, and a few things are immediately clear: the Conservatives are sliding and the Liberals are gaining. That Conservative slide is especially consistent, as their polling has been rather tight. Liberal polling is far more erratic (likely due to the leadership race), but it is clearly improving. The New Democrats have been steady, for the most part, aside from the bump after Thomas Mulcair took over.

Plotting the data like this shows how noisy it is: various polls were placing the NDP and Liberals second or third during the NDP leadership race, while they placed the NDP and Conservatives first or second after Mulcair's victory. Now, they are putting the parties in a single mass.

And this is with large samples of 1,000 people or more. The effect of smaller regional samples becomes quickly apparent when we plot the data in the same way at the regional level.

You can see this quite clearly in British Columbia. The Liberals and Greens have been relatively consistent, but even so their results vary wildly. The Conservatives and NDP have varied even more, but as the race is almost entirely between them you can see just how much the two parties overlap (you can also see a few individual Liberal results squeaking into the top of the graph). The Greens, Liberals, and NDP have been relatively steady overall, but a negative trend is clear for the Tories.

In Alberta, the Conservative lead is obvious but the negative trend is also present. Among the opposition parties, the Liberals are clearly gaining while the NDP are on a slight decline. It isn't much, but it is interesting to see how the NDP was clearly ahead of the Liberals until the fall of 2012, at which point their poll results start to get mixed up.

The Prairies are a bit of a mess, but the order of the parties is easy to see. The Conservative slide is less pronounced here, but you can see that the NDP appears to be heading south while the Liberals are gaining. You can also see that after Mulcair's victory the NDP was flirting with first place in the region, but have not done so for several months.

In Ontario, the Conservatives have been on a negative trend since the election, with their polling dropping from 40%+ to the mid-30s. The New Democrats and Liberals are jumbled together, though, with the only clear difference having been in the middle of 2012. The trend for the NDP is a positive one, but it is hard to see it in the data.

Five parties means a jumbled chart for Quebec, but even so you can easily see where the parties are. You can also see how the NDP's fortunes have ebbed and waned. You see good numbers for them after the election, sinking numbers during the leadership race, soaring numbers after Mulcair's win, and a slow decline since. It varies greatly with the trend line, but you can see the overall slide.

The mass of results for the other parties is a little more difficult to see through, but the trend lines help. For one, the Conservative results are hidden behind those of the Bloc Québécois and Liberals for most of the chart, before they slip below them more recently. That says all you need to know about that. The Bloc's numbers have been pretty steady, while the Liberals are heading northwards. You can see that the Liberals flirted a little with the NDP before Mulcair became leader, and is now doing so again (and with stronger results).

And then we come to Atlantic Canada, which understandably has the noisiest data. Sample sizes are usually the smallest in Atlantic Canada and the Prairies, but unlike in the Prairies the race here is a three-way one. That puts the parties in a bit of a tangled mess. Nevertheless, you can see the trends if you try: the Conservatives started out with the best results, then it was the NDP that moved ahead, and now it is the Liberals. The trend lines are pretty stark, with the NDP steady, the Conservatives falling steeply and the Liberals gaining. 

It is an interesting way to look at the polls. The Conservative slide is present in each region, the Liberals are gaining in most of the country, and the New Democrats are trending upwards in some parts of Canada and downwards in others. Averaging the polls out as I do on this site is one way to make some sense of it, but plotting the data this way shows how there is a different way to make sense of it. It demonstrates that the general trends are visible, even if the polls can appear to be all over the place. Sometimes, though, they leave little doubt as to what is going on.