Election polling errors across time and space

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An Author Correction to this article was published on 26 June 2020

This article has been updated

Abstract

Are election polling misses becoming more prevalent? Are they more likely in some contexts than others? Here we undertake an over-time and cross-national assessment of prediction errors in pre-election polls. Our analysis draws on more than 30,000 national polls from 351 general elections in 45 countries between 1942 and 2017. We proceed in the following way. First, building on previous studies, we show how errors in national polls evolve in a structured way over the election timeline. Second, we examine errors in polls in the final week of the election campaign to assess performance across election years. Third, we undertake a pooled analysis of polling errors—controlling for a number of institutional and party features—that enables us to test whether poll errors have increased or decreased over time. We find that, contrary to conventional wisdom, the recent performance of polls has not been outside the ordinary. However, the performance of polls does vary across political contexts and in understandable ways.

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Fig. 1
Fig. 2: Poll errors across electoral history.
Fig. 3: Poll errors in recent elections (2015–2017).

Change history

  • 26 June 2020

    An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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Acknowledgements

An earlier version of this article was presented at the Advertising Research Foundation’s ForecastxScience meeting, Google, Sunnyvale, California, 14–15 November 2017. We thank C. Kennedy, D. Rothschild, P. Sturgis and G. Terhanian for comments on earlier versions of this paper, and to Lord Lipsey and other members of the House of Lords Select Committee on Political Polling and Digital Media for their comments and questions. The funders had no role in study design, data collection and analysis, decision to publish or preparation of the manuscript.

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C.W. and W.J. developed the original study concept. W.J. and C.W. gathered and analysed the data, and drafted and revised the manuscript. W.J. wrote the computer code and generated the figures and tables in Stata.

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Correspondence to Will Jennings or Christopher Wlezien.

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Jennings, W., Wlezien, C. Election polling errors across time and space. Nat Hum Behav 2, 276–283 (2018). https://doi.org/10.1038/s41562-018-0315-6

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