Polling turnout filters might be deceptive
It has become standard practice almost all polling firms to include a weighting for turn out particularly in the final stages of a campaign.
Participants are asked to rate the chances of them voting on a scale of 1-10 and the results are used to scale up or scale down their voting intention responses.
The most radical approach is taken by Ipsos-MORI which only includes the views of those 10/10 absolutely certain to vote in its headline figures. ICM adds another dimension and scales down by 50% the views of those who say they did not vote last time.
Certainty to vote weighting is fine for the country as whole but in the key battlegrounds we have to assume that the party get out the vote operations (GOTV) will get more people out.
This is hardly surprising because after the whole point of the high octane highly intensive campaigning is to ensure that more of your potential voters actually do so.
Elsewhere, in the other 80% of seats, general election campaigns operate at a much lower tempo. Quite often party activists in the non-marginals are encouraged to put their efforts into seats other than their own.
Thus at GE2015 we are going to see a lot more focus on distributed phone banking and the parties are investing in infrastructures to make it simple to manage and ensure that databases are kept up to date – vital on polling day. A lot of this was tested at Eastleigh.
Overall we should be looking at the polls expecting that in the battlegrounds more marginal voters will vote.
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