When people consider public policy disputes, they often hear conflicting claims from scientific experts. For example, most climate change scientists say that their studies show that human behaviour is causing global warming and that if we do not reduce greenhouse gas emissions, global warming will have severe impacts on human society and the environment. In contrast, climate change sceptics argue that humans are not causing global warming and that if we sharply cut greenhouse gas emissions, we will only damage our economy.
How do people decide which scientists are telling the truth and which scientific claims to believe?
The best way to conceive of the process is not to think of it as a matter of learning from scientists, but to think of it as persuasion. A campaign to elect a candidate to office is a good model. Opposing campaigns argue in favour of their candidate, and there is no ‘objectively’ best candidate.
Credibility and beliefs
Persuasion has been a subject of research for many decades. Two previously studied causes of whether people believe persuasive messages are the credibility of the message source and whether the message content agrees with a person’s prior beliefs and values.
The source credibility hypothesis is that people are more likely to believe a message from a person or organization they trust. For example, environmentalists are more likely to believe a scientist working for an environmental organization than one who works for an oil company. The message content hypothesis is that people are more likely to believe messages that are consistent with their values and prior beliefs than inconsistent messages. For example, people who believe that offshore oil drilling is risky are more likely to accept a scientific study warning about greater risks than a study claiming that oil drilling is safe.
Unfortunately, this last hypothesis has been largely ignored in recent decades.
Our research investigated both hypotheses using an experiment embedded in a public opinion survey of California residents. The survey asked six random variations of a question about confidence in a scientific study. Respondents were told that the study was conducted by government, oil industry, or environmental group scientists, and that the study found that offshore oil drilling was either safer or riskier than previously believed.
Two findings stand out. First, we found that the largest influence on whether people believe scientific reports is whether the report is consistent with their beliefs. For example, people who oppose offshore oil drilling were far more likely to accept a study showing that oil drilling is risky than they were to accept one indicating that it is safe. This result holds up under statistical analysis with a variety of control variables, including people’s values.
Second, we found that people are more likely to believe reports that oil drilling is riskier than previously believed than they are to believe that it is safer. Regardless of people’s values or prior beliefs, they respond to warnings about potential risks.
If our research is supported when replicated in other policy areas, it does not bode well for the influence of science on public policy debates. If people tend to discount news reports about scientific studies that conflict with their preexisting beliefs, regardless of the source, then scientists will have a tough task educating the public about issues such as climate change and energy policy.
Moreover, if people tend to accept warnings about risks, regardless of their scientific support, scientists will find their public education attempts doubly difficult. This is not a conclusion that is likely to bring joy to the hearts of the scientific community.
This article is a shortened version of an article by Juliet E. Carlisle, Jessica T. Feezell, Kristy E.H. Michaud, Eric R.A.N. Smith and Leeanna Smith: The public’s trust in scientific claims regarding offshore oil drilling, Public Understanding of Science 19, 5, pp.514-527