Analyzing the polls of the US 2020 Presidential Election Campaign: A New Perspective
36 Pages Posted: 27 Aug 2023 Last revised: 2 Feb 2024
Date Written: October 23, 2023
Abstract
The poll performance of the 2020 US election has stood out as the worst in US presidential elections since 1996. National election polls also presented the largest difference in estimates between modes of administration in US elections since 2008. What happened? This article proposes a new perspective on the polls published at the national level during the campaign. It examines the 222 polls conducted from September 1st to November 2nd 2020 to assess whether they differed according to mode of administration and sampling source in the portrait they trace of what happened during the campaign and in their capacity to forecast the election results. The polls are grouped into three categories that combine mode of administration and sampling source: a) the mixed-mode polls (16% of the polls), which use multiple modes and sampling sources; b) the single-mode quasi-random polls (25%), which use one mode of administration but resort to random or quasi-random sampling sources; and c) the web polls that use exclusively opt-in panels (59%). Two types of regression analysis are performed. Local regression generates an estimate of the trends in voting intention, and multilevel analysis provides a statistical validation of these trends, all else being equal, after controlling for the polls’ dependency on pollsters and their methodological characteristics. These analyses demonstrate that the various mode-source combinations differ in their depiction of what happened during the campaign. The polls that used random or quasi-random sampling sources, whether mixed-mode or single-mode, estimate that voting intention for Joe Biden increased until mid-campaign and declined afterward. On the contrary, the web opt-in polls estimate that support for Joe Biden was stable throughout the campaign. In addition, the mixed-mode polls lead to a perfect vote forecast. A descriptive analysis of the polls conducted during the last ten days of the campaign validates these results. Almost all the mixed-mode polls and the single-mode quasi-random polls produced estimates within their margin of error or credibility interval compared to only 54% of the web opt-in polls. Other methodological practices, like resorting to multiple opt-in panels or weighting using propensity scores, are also associated with better estimates. We hypothesize that modes and sampling sources reach different voters, but none reach them all, hence the necessity to resort to mixed-modes or to vary the sampling sources. If we consider that the perfect forecasting produced by mixed-mode polls is an indication of their overall reliability, we conclude that what likely happened during the campaign is an increase and subsequent decrease in voting intention for Joe Biden. American citizens did not receive this information because the trend traced by web opt-in polls dominated the averages. Academics, media, and pollsters in the US and elsewhere need to monitor the new methods that emerged in the US 2020 election and draw lessons from their performance.
Keywords: Electoral polls; Survey methods, Election Forecasting, US 2020 presidential election, Local regression, Multilevel analysis
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