The above plot shows Canadian voting intentions between September 1st  and October 20th, ’09. The dots represent the results of individual polls. The curves represent the filtered voting intentions, that is, voting intentions with the polling error taken or filtered out. The problem of data smoothing or filtering is routinely encountered in applications such as GPS navigation and audio remastering (think of the last Beatles’ album). In the same way as the GPS navigator in your car blends data from several GPS satellites to accurately determine where you are, the above curves are the result of blending together the data from several polls (the dots in the above plot) which are conducted at close time intervals. The result is an accurate picture of the evolution of voter intentions in Canada over time.

So why bother filtering? Well, just look at the last two green dots on the lower right of the plot. They represent the support for the Green Party as polled by Nanos (+/-3.4% margin of error) and EKOS (+/-1.7% margin of error) on Oct 10th-18th and on Oct 14th-20th, respectively. These two polls show 4.6% and 11% of Green support, respectively. Is it likely that support for the Greens jumped by that much over 2 days? Of course not! That is one example of why poll filtering is needed.

The above plot shows that since September 1st, the Conservatives have rallied another 5% of all voters to their cause and their overall support now stands at 39%. At the same time, the Liberals have lost about 3% and now stand at 28%. The NDP has lost about 1% of support and they now stand at 15%. Support for both the Greens and the Bloc continues to hover around 8%-10%. Despite this dramatic shift over 50 days, voter intentions have remained fairly stable over the last week or so (last five polls). Possible explanations for this change in public opinion include:

1. 1.Micheal Ignatieff’s decision to no longer support the current government (though the Liberals have recently nuanced this position).
   

2. 2.The decision by the NDP to prop Harper’s government.
   

3. 3.The economic situation appears to be stabilizing, which favours the governing Conservatives.
   

I will be updating the output of the poll filter regularly. Check back often for an accurate and up-to-date picture of what the Canadian electorate thinks.

Feel free to add a comment to the website or to send me an email.

For technically-inclined people interested in more details on how this model works, the filter uses exponential time-varying weights for each poll. The older the poll, the less it registers in the final result. The exponential weight relation is typical in low-pass filters such as audio filters used to reduce hiss. I chose this type of filter over an averaging filter these filters have an appreciable time lag (it takes a while for a big change in the public opinion to register in the filter). Also, they do not easily account the non-uniform time intervals at which polls are taken. Feel free to drop me a line for more details.

Later!