The Implied Truth Effect: Attaching Warnings to a Subset of Fake News Stories Increases Perceived Accuracy of Stories Without Warnings

49 Pages Posted: 14 Sep 2017 Last revised: 22 Mar 2019

See all articles by Gordon Pennycook

Gordon Pennycook

University of Regina

Adam Bear

Yale University

Evan Collins

Yale University, School of Medicine, Students

David G. Rand

Massachusetts Institute of Technology (MIT)

Date Written: March 15, 2019


What can be done to combat political misinformation? One widely employed intervention involves attaching warnings to news stories that have been disputed by third-party fact-checkers. Here we demonstrate a hitherto unappreciated consequence of such warning: an “implied truth” effect whereby false stories that fail to get tagged are considered validated, and thus are seen as more accurate. Such an effect is particularly important given that it is much easier to produce misinformation than it is to debunk it. We first introduce a formal model showing that such an implied truth effect is the necessary consequence of Bayesian belief updating. In Study 1 (N = 5,271 MTurkers), we find that while warnings do lead to a modest reduction in perceived accuracy of false headlines relative to a control condition (particularly for politically concordant headlines), we also observed the hypothesized Implied Truth Effect: the presence of warnings caused untagged headlines to be seen as more accurate than in the control. In Study 2 (N = 1,568 MTurkers), we find the same effects in the context of decisions about which headlines to consider sharing on social media. We also find that attaching verifications to some true headlines – which removes the ambiguity about whether untagged headlines have not been checked or have been verified – eliminates, and in fact slightly reverses, the Implied Truth Effect. Together, these results challenge theories of motivated reasoning, while identifying a new challenge for the policy of using warning tags to fight misinformation.

Note: A previous version of this working paper was titled “Assessing the effect of “disputed” warnings and source salience on perceptions of fake news accuracy”. To allow for a more detailed treatment of both issues, the source salience aspect of the previous manuscript (former Study 2) has been removed from this updated version and will be re-posted as a part of a separate paper investigating source effects.

Keywords: fake news, news media, social media, fact-checking, misinformation, source credibility

Suggested Citation

Pennycook, Gordon and Bear, Adam and Collins, Evan and Rand, David G., The Implied Truth Effect: Attaching Warnings to a Subset of Fake News Stories Increases Perceived Accuracy of Stories Without Warnings (March 15, 2019). Available at SSRN: or

Gordon Pennycook

University of Regina ( email )

3737 Wascana Parkway
Regina, Saskatchewan S4S OA2 S4S 0A1

Adam Bear

Yale University ( email )

2 Hillhouse Ave
New Haven, CT 06511
United States


Evan Collins

Yale University, School of Medicine, Students ( email )

New Haven, CT
United States

David G. Rand (Contact Author)

Massachusetts Institute of Technology (MIT) ( email )

77 Massachusetts Avenue
50 Memorial Drive
Cambridge, MA 02139-4307
United States


Register to save articles to
your library


Paper statistics

Abstract Views
PlumX Metrics