Monday, September 15, 2008

Weighting of Polls

I was asked how I weight the polls. To give you an example, here is how I weighted the last few days.

Adjusting for size:

  • Ekos x 5.0
  • Harris x 2.0
  • Nanos x 2.0
  • Angus Reid x 1.15
  • Ipsos x 1.0

I give five times the weight to the Ekos results because theirs was a poll of 5000 people. I aggregate the Nanos and Harris/Decima daily tracking polls and give them a weight as if they were one poll each of 2000 people. For Ipsos and Angus Reid, the weighting reflects the number of respondents in their one poll.

Doing this gives the following results:

  • Conservatives - 37.4%
  • Liberals - 26.8%
  • NDP - 17.1%
  • Bloc - 7.9%
  • Greens - 10.2%

It is important to do this because Harris/Decima has a new tracking result everyday and seems to have the Conservatives higher than the rest and Nanos has a new result each day but with the Liberals higher than the rest. Neither company asked as many people as Ekos did and therefore should not hold as much weight in the averaging.

The above results show the Greens as the big winners and the Liberals and Bloc both suffering.

If we look at the CTV/Globe Battleground ridings and average out the results over a week, which they are not doing I think should be, we see some clear trends.

In BC the Conservatives have gained only marginally on 2006, just over two percentage points. But their gain is more than matched by a fall for the NDP and Liberals.

The NDP is down marginally but the Liberals are down more than a 1/4 of their vote. This is a huge problem for them as they hold six of the ten BC Battleground ridings.

In Ontario the Conservatives have a much bigger gain in the vote, they are up almost six percentage points on 2006.

The Liberals have lost 1/4 of their vote in Ontario as they have done in BC.

The NDP is also down from their 2006 support.

In Quebec Conservatives are up more than either BC or Ontario and very close to the levels of Bloc support. The Bloc has seen their vote fall by 20%.

The Liberals once again are down a 1/4 of their vote in Quebec.

These trends in the battleground ridings are very bad news for Stephane Dion. If this were to extrapolate to the rest of the country, 22.5% support for the federal Liberals is realistic.

1 comment:

Anonymous said...

This is a brilliant post. I wish all bloggers had your common sense when looking at polls. Congratulations.