How to Debate a Science Denier

The U.S. is currently experiencing the largest outbreak of measles since 1992. According to the Centers for Disease Control and Prevention, there have been more than 1,000 confirmed cases since January. Scientific research overwhelmingly supports the use of vaccinations against measles. Mistaken worries about their harms has led to a reduction in the number of immunizations, contributing to the return of a disease that was said to be eliminated in the U.S. in 2000. “There is an urgent need for good strategies to counter science deniers, because we see how much damage they can do,” says Cornelia Betsch, a professor of health communication at the University of Erfurt in Germany.

Betsch and Philipp Schmid, a doctoral student in her lab, decided to examine two strategies for counteracting the spread of misinformation in public debates: The first, called topic rebuttal, opposes misinformation about a given issue with established facts. Another, known as technique rebuttal, involves unmasking methods that science deniers use to mislead their audience. In a study published on June 24 in Nature Human Behaviour, the two researchers report that both methods reduced the influence of science deniers—especially among individuals who were already vulnerable to antiscience beliefs.

Technique rebuttals are a particularly effective and economic tool, according to Betsch, because methods used by science deniers tend to be very similar. One such technique, called selectivity, involves cherry-picking isolated papers that support an unconventional viewpoint or discrediting a few flawed papers to cast doubt on an entire field of science. Another method raises impossible expectations for science—arguing, for example, that rejecting vaccination is acceptable because vaccines are not 100 percent safe, although science can never guarantee that certainty for any medical product. Even routinely used medications such as aspirin come with potential risks.

“If you learn [these] techniques once, then you can use them on very different topics,” Betsch says. “The problem with topic rebuttal is that you really have to know the science well—and that might be a big ask, because there’s a ton of research, and it’s sometimes difficult to know everything.”

Betsch and Schmid examined how well these two techniques could counter antiscience rhetoric in six online experiments that collected data from 1,773 respondents. In the first trial, the pair played an audio recording of a debate about vaccination to a group of German undergraduate students. The researchers randomly assigned participants to one of four conditions—no rebuttal, topic rebuttal, technique rebuttal or both. They measured attitudes toward vaccines and the intention to vaccinate before and after the recordings. The duo then repeated this protocol across different conditions: in samples of the general population in both Germany and the U.S. and in an alternative presentation format of written arguments.

The results of these experiments revealed that exposure to a science denier diminished participants’ intention to get vaccinated. Both technique and topic rebuttal, however, were able to reduce this influence—and appeared to be equally effective. But combining the two approaches did not seem to provide additive benefits. “Overall, I think that’s a positive result,” says John Cook, a cognitive scientist at George Mason University, who did not take part in the study. “This work gives communicators confidence that they can use different approaches and still be effective.”

When Betsch and Schmid assessed the effects of political ideology and prior beliefs, they discovered that the influence of the deniers was higher in individuals who had low confidence in vaccinations and in those in the U.S. who identified as conservative. People from these groups also benefited the most from the rebuttals.

In one of the six experiments, the investigators examined attitudes toward climate change—and found much weaker effects. According to Betsch, this result is likely because that specific test only assessed undergraduate students in Germany. Participants in that trial were not influenced much by the antiscience rhetoric in the first place, which meant there was very little room for change. “I think if you replicate this in the U.S., it would be different,” Betsch says. “[In Germany] it’s just not common to be a climate change denier.”

These results counter a so-called backfire effect, in which debating a science denier may actually reinforce people’s misconceptions. While a handful of studies have provided evidence that such unintended results may be widespread, more recent investigations have found that these effects may be limited to specific circumstances—such as among people whose fundamental beliefs about a functioning society are challenged by the new information. “There was a period where everyone, especially psychologists and political scientists, were perhaps overselling the backfire effect,” says Sander van der Linden, a social psychologist at the University of Cambridge, who was not involved with the research. “This study once again shows that this is not something that happens all the time.”

Concerns about the backfire effect have deterred some people from entering into public discussions with science deniers, Betsch says. But, she adds, her and Schmid’s findings show that even in falsely balanced debates—in which opposing viewpoints are presented despite evidence overwhelmingly supporting only one argument—it is important that a debater who can counter antiscience arguments is present. 

Although rebuttals effectively reduced the influence of science deniers, van der Linden says that it is important to note that they did not completely eliminate the effect of exposing people to these denials. “The practical problem with this approach is that it’s all reactive,” he adds. “The limitation is: if you come after the fact, it’s likely worse than [intervening] preemptively.”

In recent years, researchers have started to investigate so-called inoculation techniques, which aim to help people identify methods commonly used to spread falsehoods before they are exposed to misinformation. Van der Linden and his colleagues have applied this approach to an online game called Bad News, which seeks to teach users media literacy. Preliminary evidence shows that playing this game makes people less susceptible to fake news, and van der Linden’s team is currently investigating how effective this intervention is in large groups of people with different cultural backgrounds.

Inoculating people against false facts should be the priority, van der Linden says. But this is not always possible because misinformation is so widespread. “Sometimes you have no other options,” he adds. “And what they’re showing is that [these rebuttals] are an effective second line of defense.”



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