In Quebec, the top pollster for the Bloc Québécois is Harris-Decima, who polls them 2.8 points higher than the average of other pollsters. The worst is CROP, which polls them 3.7 points below average.
The top pollster for the Liberals is Environics, polling them 5.9 points higher than average. The worst is EKOS, which polls them 3.5 points lower than the average.
The top pollsters for the Conservatives are Ipsos-Reid and Nanos, polling them at 1.4 points higher than average. The worst is Environics, 4.0 points lower than the average.
The top pollster for the New Democrats is CROP, 3.4 points higher than average. The worst is Harris-Decima, 2.0 points lower than average.
And for the Greens, the top pollster is Strategic Counsel, 6.2 points higher than average. The worst is Nanos, 3.0 points lower than average.
The most consistent pollsters seem to be Ipsos-Reid, with no more than a 1.6 point difference than the average, and Angus-Reid, with no more than a 2.2 point difference.
Just for fun, let's take Angus-Reid's poll from Monday and apply these numbers to it:
Bloc Québécois - 38% = 35.8%
Liberals - 24% = 25.7%
New Democrats - 16% = 17.3%
Conservatives - 16% = 16.5%
Greens - 6% = 7.6%
This gives an indication of how well the NDP did in this Angus-Reid poll.
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. 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.
