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The impact of weightings and adjustments on the accuracy of the final polls in 2010.

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Presentation on theme: "The impact of weightings and adjustments on the accuracy of the final polls in 2010."— Presentation transcript:

1 The impact of weightings and adjustments on the accuracy of the final polls in 2010

2 The problem Bias to LabourBias to Conservative

3 Modifications to method post ) Adjusting for turnout 1) Adjusting for turnout –Weights according to certainty to vote. (Most usually mark out of ten) 2) Past vote weighting 2) Past vote weighting –Weighting recall of past votes towards result last time 3) Spiral of Silence 3) Spiral of Silence –“People who think their views are in a minority may become inclined to silence”

4 What we looked at 1) How accurate were the polls as measured by average error and lead 1) How accurate were the polls as measured by average error and lead Average difference between 4 estimates (3 large parties plus others) and result Average difference between 4 estimates (3 large parties plus others) and result 2) Whether published percentages closer to outcome than unweighted data? 2) Whether published percentages closer to outcome than unweighted data? 3) For some telephone polls we look at the impact of each stage of weighting and adjustment 3) For some telephone polls we look at the impact of each stage of weighting and adjustment

5 What this approach can/cannot tell us Can tell us Can tell us –Representativeness of original unweighted samples –Comparison of unweighted/weighted data and outcome, shows efficacy of methods employed Can’t tell us Can’t tell us –Did shy voters turn out for party supported last time? –Was late swing a factor?

6 Telephone Polls. Accuracy of Published results (Average Error) Percent error

7 Telephone Polls. Error in lead (Average Error) Lead error

8 Online Polls. Accuracy of Published results (Average Error) Percent error

9 Online Polls. Error in lead (Average Error) Lead error

10 Estimate of lead. All Polls

11 Face to Face poll. Accuracy of Published results (Average Error)Error in lead = 1%

12 Patterns Every poll overestimated the LibDem share Every poll overestimated the LibDem share –This was the major story of the campaign. Was it real? Telephone polls for most part more accurate than online Telephone polls for most part more accurate than online –But slight tendency by most polls (however conducted) to overstate Conservative lead (AT LAST!), and overstate LibDem support –All online polls overstated LibDems and understated both Con and Lab

13 So did weighting/adjustment lead to more accurate estimates?

14 Weighting ICM – Past Vote, turnout, shy ICM – Past Vote, turnout, shy Populus - Past Vote, turnout, shy Populus - Past Vote, turnout, shy Comres – Past Vote, turnout Comres – Past Vote, turnout Angus Reid - Past Vote, turnout Angus Reid - Past Vote, turnout Harris – Propensity Score, turnout Harris – Propensity Score, turnout YouGov – Party identification, turnout YouGov – Party identification, turnout Ispos – Turnout Ispos – Turnout Opinium – Turnout Opinium – Turnout

15 Telephone Polls. Effect of weighting and adjustment (Average Error) WorseBetter

16 Online Polls. Effect of weighting and adjustment (Average Error) WorseBetter

17 Effect of each element of weighting

18 To be fair ……. Accept weighting as a package Accept weighting as a package Unfair to unpick weighting schemes, a combination of corrections agencies concerned think appropriate. Unfair to unpick weighting schemes, a combination of corrections agencies concerned think appropriate. Can’t look at each possible combination of weighting variables or each individually (too many) Can’t look at each possible combination of weighting variables or each individually (too many)

19 Average error at each stage of weighting

20 Error in lead at each stage of weighting Bias to LabourBias to Conservative

21 Errors pulling at the polls Past VotesShy voters Telephone Polls 2010 Telephone Polls Past VotesShy voters 2010 Online Polls Past VotesShy voters

22 Conclusions 2010, unweighted data just as good as weighted data 2010, unweighted data just as good as weighted data –But estimates of lead would have been worse –A brave or foolish pollster who would now abandon adjustments, as errors may not cancel each other in future Next time may have shy Tories/LibDems again Next time may have shy Tories/LibDems again But new problem is over estimate of LibDems But new problem is over estimate of LibDems Only really find their voice again during next election campaign Only really find their voice again during next election campaign


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