Accessible Requires Authentication Published by De Gruyter August 21, 2017

Understanding the 2016 US Presidential Polls: The Importance of Hidden Trump Supporters

Peter K. Enns, Julius Lagodny and Jonathon P. Schuldt

Abstract

Following Donald Trump’s unexpected victory in the 2016 US presidential election, the American Association for Public Opinion Research announced that “the polls clearly got it wrong” and noted that talk of a “crisis in polling” was already emerging. Although the national polls ended up being accurate, surveys just weeks before the election substantially over-stated Clinton’s lead and state polls showed systematic bias in favor of Clinton. Different explanations have been offered for these results, including non-response bias and late deciders. We argue, however, that these explanations cannot fully account for Trump’s underperformance in October surveys. Utilizing data from two national polls that we conducted in October of 2016 (n>2100 total) as well as 14 state-level polls from October, we find consistent evidence for the existence of “hidden” Trump supporters who were included in the surveys but did not openly express their intention to vote for Trump. Most notably, when we account for these hidden Trump supporters in our October survey data, both national and state-level analyses foreshadow Trump’s Election Day support. These results suggest that late-breaking campaign events may have had less influence than previously thought and the findings hold important implications for how scholars, media, and campaigns analyze future election surveys.


Corresponding author: Peter K. Enns, Associate Professor, Department of Government, Executive Director, Roper Center for Public Opinion Research, Cornell University, Ithaca, USA

Appendix 1: State Polls Analyzed in Figure 1

As explained in the text, the state polls analyzed in Figure 1 were selected based on the following criteria: a sample of likely voters, live telephone interviews, in the field around early October, and included vote intentions for the presidential and Senate candidate. If more than one survey in a single state met these criteria, we selected the survey conducted closest to October 1. Additional survey details appear below in Table A.1.

Table A.1:

Details for State Surveys Analyzed in Figure 1

StatePolling organizationDates in the fieldSample sizeLink
ArizonaEmerson10/2–10/4600http://www.realclearpolitics.com/docs/-2016/Emerson_final_Press_Release_-and_Toplines_Fl-Nv-RI-AZ-_10.5_.pdf
ColoradoMonmouth9/29–10/2400https://www.monmouth.edu/WorkArea/DownloadAsset.aspx?id=40802211216
FloridaNBC/WSJ/Marist10/3–10/5700http://www.nbcnews.com/politics/-2016-election/polls-clinton-ahead-florida-pennsylvania-n662076
GeorgiaLandmark communications10/11–10/121400https://www.realclearpolitics.com/docs/2016/Landmark_Poll_Georgia_Statewide_Oct_11-12_2016.pdf
IllinoisThe Simon Poll/SIU9/27–10/2865http://www.realclearpolitics.com-/docs/2016/Simon-SIU_Poll_Sept_2016.pdf
IndianaWTHR/Howey politics10/3–10/5600http://www.wthr.com/article/-exclusive-wthrhpi-poll-clinton-trump-presidential-race-tightens
IowaDesMoines register10/3–10/6642http://www.desmoinesregister.com/-story/news/politics/iowa-poll/2016/-10/10/iowa-poll-grassley-leads-judge-in-senate-race-by-17-points/91824228/
MissouriMonmouth10/9–10/11406http://www.monmouth.edu/polling-institute/reports/MonmouthPoll_MO_101216/
NevadaCBS News/YouGov10/12–10/14996https://www.scribd.com/document/-327758568/CBS-News-Battleground-Tracker-Nevada-Oct-16#from_embed
New HampshireUMass Lowell/7 News10/7–10/11517https://www.uml.edu/docs/TOPLINE-UMassLowell-7NEWS NH GENERAL20161013_tcm18-262711.pdf
North CarolinaNBC/WSJ/Marist10/10–10/12743http://maristpoll.marist.edu/wp-content/misc/NCpolls/NC161010/NBCNews_WSJ_Marist Poll_North-CarolinaTablesofAdultsandRegisteredVoters_October2016.pdf–page=3
OhioMonmouth10/1–10/4405http://www.monmouth.edu/polling-institute/reports/MonmouthPoll_OH_100516/
PennsylvaniaNBC/WSJ/Marist10/3–10/6709http://www.nbcnews.com/politics/2016-election/polls-clinton-ahead-florida-pennsylvania-n662076
WisconsinCBS News/YouGov10/5–10/7993https://www.scribd.com/document/-326944222/CBS-News-Battleground-Tracker-Wisconsin-Oct-9-2016-#from_embed

Appendix 2: National Polls Analyzed in Figure 2

The data in Figure 2 come from the Roper Center for Public Opinion Research iPOLL database. The survey questions reported in Figure 2 typically followed the format, “If the (2016) presidential election were being held today and the candidates were Hillary Clinton and Tim Kaine, the Democrats, Donald Trump and Mike Pence, the Republicans, Gary Johnson and Bill Weld of the Libertarian Party, and Jill Stein and Ajamu Baraka of the Green Party, for whom would you vote? Would you lean toward Clinton and Kaine, Trump and Pence, Johnson and Weld, or Stein and Baraka?” After asking this initial vote intention question, several surveys followed up with respondents who indicated a third party candidate, do not know, or no answer, by asking, “If the only candidates were Hillary Clinton and Tim Kaine the Democrats and Donald Trump and Mike Pence the Republicans, for whom would you vote?” To ensure the results in Figure 2 are as representative as possible, we include the results from both formats when they are available. Additional survey details follow.

  • USABC.102316.R03: ABC News. ABC News Poll, Oct, 2016 [survey question]. USABC.102316.R03. ABC News [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USABC.102516.R03: ABC News. ABC News Poll, Oct, 2016 [survey question]. USABC.102516.R03. ABC News [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USABC.102316.R05: ABC News. ABC News Poll, Oct, 2016 [survey question]. USABC.102316.R05. ABC News [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USABC.102516.R05: ABC News. ABC News Poll, Oct, 2016 [survey question]. USABC.102516.R05. ABC News [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USABC.102616.R03: ABC News. ABC News Poll, Oct, 2016 [survey question]. USABC.102616.R03. ABC News [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USABC.102616.R05: ABC News. ABC News Poll, Oct, 2016 [survey question]. USABC.102616.R05. ABC News [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USABCWP.102716.R04: ABC News/Washington Post. ABC News/Washington Post Poll, Oct, 2016 [survey question]. USABCWP.102716.R04. ABC News/Washington Post [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USABCWP.102716.R03: ABC News/Washington Post. ABC News/Washington Post Poll, Oct, 2016 [survey question]. USABCWP.102716.R03. ABC News/Washington Post [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USABCWP.101616.R05: ABC News/Washington Post. ABC News/Washington Post Poll, Oct, 2016 [survey question]. USABCWP.101616.R05. ABC News/Washington Post [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USABCWP.101616.R03: ABC News/Washington Post. ABC News/Washington Post Poll, Oct, 2016 [survey question]. USABCWP.101616.R03. ABC News/Washington Post [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USARG.102116A.R01: American Research Group. American Research Group Poll, Oct, 2016 [survey question]. USARG.102116A.R01. American Research Group [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USAP.102616G.R05: Associated Press. Associated Press/GfK Knowledge Networks Poll, Oct, 2016 [survey question]. USAP.102616G.R05. GfK Knowledge Networks [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USPRRI.101916.R03: Brookings Institution. PRRI/Brookings Survey, Oct, 2016 [survey question]. USPRRI.101916.R03. PRRI [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USORC.20161023.Q05: Cable News Network. CNN/ORC International Poll, Oct, 2016 [survey question]. USORC.20161023.Q05. ORC International [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USORC.102416.R01A: Cable News Network. CNN/ORC International Poll, Oct, 2016 [survey question]. USORC.102416.R01A. ORC International [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USCBS.101716.R04: CBS News. CBS News Poll, Oct, 2016 [survey question]. USCBS.101716.R04. CBS News [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USCBS.101716.R07: CBS News. CBS News Poll, Oct, 2016 [survey question]. USCBS.101716.R07. CBS News [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USPSRA.102716K.RV03: Henry J. Kaiser Family Foundation. Kaiser Health Tracking Poll, Oct, 2016 [survey question]. USPSRA.102716K.RV03. Princeton Survey Research Associates International [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USPSRA.102716K.RV02: Henry J. Kaiser Family Foundation. Kaiser Health Tracking Poll, Oct, 2016 [survey question]. USPSRA.102716K.RV02. Princeton Survey Research Associates International [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USPSRA.102716.R011A: Pew Research Center for the People & the Press. Pew Research Center for the People & the Press Political Survey, Oct, 2016 [survey question]. USPSRA.102716.R011A. Princeton Survey Research Associates International, Abt SRBI [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USPSRA.102716.R010A: Pew Research Center for the People & the Press. Pew Research Center for the People & the Press Political Survey, Oct, 2016 [survey question]. USPSRA.102716.R010A. Princeton Survey Research Associates International, Abt SRBI [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USQUINN.101916.R01: Quinnipiac University Polling Institute. Quinnipiac University Poll, Oct, 2016 [survey question]. USQUINN.101916.R01. Quinnipiac University Polling Institute [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USQUINN.100716.R02: Quinnipiac University Polling Institute. Quinnipiac University Poll, Oct, 2016 [survey question]. USQUINN.100716.R02. Quinnipiac University Polling Institute [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USQUINN.100716.R01: Quinnipiac University Polling Institute. Quinnipiac University Poll, Oct, 2016 [survey question]. USQUINN.100716.R01. Quinnipiac University Polling Institute [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

  • USPRRI.101116.R04: The Atlantic. PRRI/The Atlantic Survey, Oct, 2016 [survey question]. USPRRI.101116.R04. PRRI [producer]. Cornell University, Ithaca, NY: Roper Center for Public Opinion Research, iPOLL [distributor], accessed Jun-13-2017.

Appendix 3: MRP Results for All 11 Swing States

Figure 4 in the text reported our MRP estimates and the actual vote share for the seven swing states with 10 or more electoral college votes. Figure A1 presents the results for all 11 swing states. Not surprisingly, our MRP estimates are much less accurate with the four states with fewer than 10 electoral college votes (CO, IA, NH, and NV). These states, after all, have smaller populations and are the least well represented in our surveys. Nevertheless, the key result holds. Unlike state surveys, which consistently underestimated Trump support, even when we consider all 11 swing states, our estimates do not reflect “correlated errors.” Our estimates (hollow dots) over-state Trump’s actual vote share (solid dots) in five states and underestimate Trump support in six states. Although more data would certainly improve our estimates, by employing MRP with one national-level survey from October, we do not systematically underestimate Trump support.

Figure A1: Trump support in October based on our GfK poll (solid dots) and actual vote support (hollow diamonds) for the 11 battleground states. Horizontal bars reflect 95% uncertainty estimates. For NC, the MRP estimate and actual vote overlap obscuring the hollow diamond.

Figure A1:

Trump support in October based on our GfK poll (solid dots) and actual vote support (hollow diamonds) for the 11 battleground states. Horizontal bars reflect 95% uncertainty estimates. For NC, the MRP estimate and actual vote overlap obscuring the hollow diamond.

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Article note:

A previous version of this paper was presented at the 2017 Annual Conference of the American Association for Public Opinion Research in New Orleans, LA. We would like to thank Claudia Deane, Gary Langer, Sam Wang, Kathleen Weldon, and Chris Wlezien for helpful comments. We also thank GfK and Cornell’s Survey Research Institute for their support and Alex Rauter for his contribution to the surveys.

Published Online: 2017-8-21
Published in Print: 2017-10-26

©2017 Walter de Gruyter GmbH, Berlin/Boston