New research published in Nature Human Behaviour casts doubt on a widely cited study, which found that conservative people tend to have stronger physiological reactions to threatening stimuli. The three replications of the original study failed to find evidence for this, suggesting that conservatives and liberals do not respond differently to threat.

“In 2008, a group of researchers published an article in Science (here it is without a paywall) that found political conservatives have stronger physiological reactions to threatening images than liberals do,” explained study author Bert N. Bakker (@bnbakker), an assistant professor at the Amsterdam School of Communication Research at the University of Amsterdam.

“In 2014, we started studying the physiological basis of political attitudes — two of us in Amsterdam and two of us in Philadelphia. We had raised funds to create labs with expensive equipment for measuring physiological reactions, because we were excited by the possibilities that the 2008 research opened for us.”

“Our intention in these first studies was to try the same thing in order to calibrate our new equipment. Yet, we quickly realized that we could not replicate the original association between physiological responses to threat and conservatism. That is the moment we realized that we should conduct a more systematic replication study and try to publish this,” Bakker said.

In the original study, the researchers measured skin conductance levels in 46 adult participants with strong political beliefs as they were exposed to sudden noises and threatening visual images. In particular, they monitored electrical activity of the sweat glands in the skin, which is an indication of the state of arousal of the sympathetic nervous system.

Those researchers found that participants with stronger physiological reactions to the noises and threatening images tended to also support more politically conservative policies.

“Particular physiological responses to threat could cause the adoption of certain political attitudes, or the holding of particular political attitudes could cause people to respond in a certain physiological way to environmental threats, but neither of these seems probable. More likely is that physiological responses to generic threats and political attitudes on policies related to protecting the social order may both derive from a common source,” wrote the authors of the original study.

The findings received a significant amount of media coverage. The authors of the new replication studies observed that it continues to be cited by publications such as CNN, The New York Times, the BBC, and Vox.

But two conceptual replications conducted by Bakker and his colleagues, one with 352 American participants and one with 81 Dutch participants, failed to find the same result.

“We conducted two studies where we used conceptually similar images and measures of ideology. We found no evidence for the claim that conservatives have stronger physiological responses to threats compared to liberals,” he told PsyPost.

The researchers then conducted a direct replication of the study with another 202 American participants.

“We conducted a preregistered replication in which we used the original threatening images used by Oxley et al. and a very closely related measure of ideology. With roughly four times as many participants in our lab, we found no evidence that conservatives have a stronger physiological response to threat compared liberals. To conclude, we find no evidence for the original claim published in Science,” Bakker explained.

“We conducted an extensive number of robustness checks to assess whether the association between the sensitivity to threat and ideology might be lurking somewhere in our data. But we found no indication that alternative model specifications or moderators condition our results.”

“That said, we are left with an important theoretical puzzle. Our study aligns with a small but growing body of literature that suggests that there might not be deep-seated psychological differences between liberals and conservatives. We hope for more research that addresses the question if and when there are physiological differences between liberals and conservatives,” Bakker added.

The study, “Conservatives and liberals have similar physiological responses to threats“, was authored by Bert N. Bakker, Gijs Schumacher, Claire Gothreau, and Kevin Arceneaux.