Monday, October 11, 2010

Polling House Effects Update

What better day to update the house effects chart than a slow and quiet Thanksgiving Monday. I've updated Ipsos-Reid and CROP, incorporating data from September 2010.

Ipsos-Reid is the most favourable pollster for the Conservatives, polling them at an average of 3.5 points higher than other pollsters. They are tied with Environics as the least favourable NDP pollster, polling them at an average of 2.2 points low than other pollsters. In Quebec, however, they are one of the pollsters with the least amount of variation from their competitors.

CROP is the best pollster for the Conservatives in Quebec, polling them at an average of 2.2 points higher than other pollsters. They are also the best for the NDP, putting them at an average of 3.9 points higher. They are the worst for the Bloc Québécois, polling them at an average of 4.2 points lower than others.

We'll use the new house effect numbers to "correct" the latest polls from Ipsos-Reid and CROP, taken at the end of September. First, Ipsos-Reid's national numbers:

Conservatives 35% = 31.5%
Liberals - 29% = 29.7%
New Democrats - 12% = 14.2%
Greens - 12% = 12.7%
Bloc Québécois - 11% = 11%

And now Quebec:

Bloc Québécois - 39% = 37.5%
Liberals - 22% = 22.3%
New Democrats - 16% = 16.4%
Conservatives - 17% = 15.8%
Greens - 6% = 6.1%

While this doesn't change the situation in Quebec very much, it does show a much closer race at the national level.

Now CROP in Quebec:

Bloc Québécois - 32% = 36.2%
Liberals - 23% = 23.8%
Conservatives - 23% = 20.8%
New Democrats - 18% = 14.1%
Greens - 4% = 6.7%

This still has the Conservatives at a much higher level than most other pollsters, but the Bloc numbers look a lot more realistic.

The chart below tracks how each pollster tends to lean when calculating support levels for the various parties, as compared to the average polling results from other pollsters each month. This does not necessarily equate to a deliberate bias, but instead is more reflective of the polling methods used - the "house effects". This is also not a scientific calculation of any kind, but it does give an indication of how each pollster tends to compare to others.

The following chart shows each pollster's average variation from other polling firms. The numbers are the amount of percentage points a particular pollster favours or disfavours that particular party compared to other pollsters over a similar period of time.