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An assessment of the causes of the errors in the 2015 UK general election opinion polls

Sturgis, P; Kuha, J; Baker, N; Callegro, M; Fisher, S; Green, J; Jennings, W; ... Smith, P; + view all (2018) An assessment of the causes of the errors in the 2015 UK general election opinion polls. Journal of the Royal Statistical Society: Series A (Statistics in Society) , 181 (3) pp. 757-781. 10.1111/rssa.12329. Green open access

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Abstract

The opinion polls that were undertaken before the 2015 UK general election underestimated the Conservative lead over Labour by an average of 7 percentage points. This collective failure led politicians and commentators to question the validity and utility of political polling and raised concerns regarding a broader public loss of confidence in survey research. We assess the likely causes of the 2015 polling errors. We begin by setting out a formal account of the statistical methodology and assumptions that are required for valid estimation of party vote shares by using quota sampling. We then describe the current approach of polling organizations for estimating sampling variability and suggest a new method based on bootstrap resampling. Next, we use poll microdata to assess the plausibility of different explanations of the polling errors. Our conclusion is that the primary cause of the polling errors in 2015 was unrepresentative sampling.

Type: Article
Title: An assessment of the causes of the errors in the 2015 UK general election opinion polls
Open access status: An open access version is available from UCL Discovery
DOI: 10.1111/rssa.12329
Publisher version: https://doi.org/10.1111/rssa.12329
Language: English
Additional information: © 2017 The Authors Journal of the Royal Statistical Society: Series A (Statistics in Society) Published by John Wiley & Sons Ltd on behalf of the Royal Statistical Society. This is an open access article under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/).
Keywords: Election polling, Late swing, Quota sampling, Turnout weighting, Turnout weighting
UCL classification: UCL
UCL > Provost and Vice Provost Offices > UCL SLASH
UCL > Provost and Vice Provost Offices > UCL SLASH > Faculty of S&HS
UCL > Provost and Vice Provost Offices > UCL SLASH > Faculty of S&HS > Dept of Political Science
URI: https://discovery.ucl.ac.uk/id/eprint/10066361
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