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Is it safe to past vote weight?

Is it safe to past vote weight?. John Curtice. Why past vote weight?. Principal aim of opinion polls is to secure accurate estimates of vote intention – but have exhibited bias to Lab since 1987.

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Is it safe to past vote weight?

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  1. Is it safe to past vote weight? John Curtice

  2. Why past vote weight? • Principal aim of opinion polls is to secure accurate estimates of vote intention – but have exhibited bias to Lab since 1987. • Demographics are nowadays relatively weakly related to vote, and weighting thereby cannot be relied upon to ensure accurate estimates • Vote at last election (‘past vote’) is strongly related to current vote intention and distribution is known • So makes sense to past vote weight!

  3. However… • People may forget or misremembered how they voted last time (‘recall error’) • And may do so non-randomly • In particular, may be inclined to avoid cognitive dissonance by aligning past vote with current preference • And to forget more ‘esoteric’ choices • In which case past vote weighting could simply make a good poll bad.

  4. Himmelweit, Biberian and Stockdale • British Journal of Political Science 1978 • Longitudinal study of young men 1962-74 (N=450) • Asked after each election how voted – and in 1970 (N=365) and October 1974 (N=246) asked to recall vote at two previous elections. • Results of recall compared with reported vote immediately after election.

  5. Butler and Stokes • 1963-64-66-70 panel study. • Asked how voted immediately after each election • And in 1970 also asked to recall 1964 and 1966 vote • N=846, and originally demographically representative

  6. Accuracy of Recall

  7. Aligning with current vote

  8. Some votes harder to remember!

  9. Perhaps? • People less likely to align recall vote with vote intention than with reported vote at the last election? • Not least because less time elapsed • Liberal Democrat no longer an ‘esoteric choice’ – more votes and stronger organisational presence.

  10. British Election Panel Studies • Followed panel of voters through 1992-7 (N=1,347) and 1997-2001 (N=1,594) parliaments • Reported vote obtained in weeks after election • Recall vote asked annually thereafter, including after next election

  11. Accuracy of Recall

  12. Aligning with current vote intention

  13. What Himmelweit did not show

  14. Did I really vote Lib Dem? - 1

  15. Did I really vote Lib Dem? - 2

  16. But consider… • Assume Con got 40% at last election; Lib Dem 20%. • Say 10% of those who voted Lib Dem last time now mistakenly claim that they voted Conservative. • Only requires 5% of those who voted Con last time to claim mistakenly they voted Lib Dem to balance the error. • So more forgetful Lib Dems ≠ fewer Lib Dems

  17. The totals compared - 1

  18. The totals compared - 2

  19. Conclusion - Aligning • Those who misremember do have a tendency to align their recall vote with their current vote intention • But most people do not misremember • And most who have changed their allegiance since the last election do not align their recall vote with their current preference

  20. Conclusion – ‘Esoteric’ Choices • People are still more likely to forget voting Lib Dem (or abstaining or voting for any ‘other) than Con or Lab • But because they represent a smaller poll of voters, they may still not be underrepresented in distribution of recall vote • So past vote weighting much ‘safer’ than Himmelweit et al suggested

  21. However… • Past vote weighting cannot deal with any bias amongst those who do not have a past vote • The impact of recall error apparently varies – across parties and parliaments • So not necessarily adequately taken into account by applying a constant ‘discount’ factor - as is current common practice • Need continuously updated panel – like BEPS. A role for Understanding Society?

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