More people are likely to believe scientific studies claiming that oil drilling is riskier, not safer, than was previously thought, according to a new study of attitudes in California. What's more the findings, which appear in the journal Public Understanding of Science (PUS), published by SAGE, show that scientists' efforts to influence public opinion have a limited effect.

Authors Jessica Feezell and Eric Smith, both from the University of California, Santa Barbara, together with Juliet Carlisle of Idaho State University, Kristy E.H. Michaud from California State University, Northridge and Los Angeles media consultant Leeanna Smith think that prior beliefs may turn out to play a critical role in many policy disputes, muting the influence of scientific studies.

"This is not a conclusion that is likely to bring joy to the hearts of the scientific community," says Smith. But how do people decide which scientific claims and which experts to believe?

Some social scientists hold that people most often believe claims by experts from organizations that line up with their own personal political views -- this is the source credibility hypothesis. An alternative view -- the content hypothesis -- claims that people are most likely to accept a scientific claim if it supports their existing views, regardless of the source.

Psychologists have been looking at these hypotheses since the 1950s, but in recent decades the content hypothesis has been all but forgotten in policy research. The investigators behind this PUS paper believe its time for a content hypothesis revival -- specifically when it comes to views on offshore oil rigs.

The researchers used an experiment embedded in a 2002 public opinion survey of 1,475 Californians to assess the confidence people have in reports about safety studies on offshore oil drilling along the California coast. Californian voters are well versed in the debate about oilrig safety: resistance to offshore oil drilling began in response to the very first offshore operation in California in 1896 and has been political hot potato ever since.

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Interviewees were each asked a question, including six variables that were randomly shuffled. The question allowed researchers to evaluate both the source and the content effects at the same time. Interviewees were also asked about their core values -- self-identified ideology (liberal Vs. conservative), party identification, individualism, and egalitarianism.

Egalitarianism and individualism are both core American values, also central to most societies worldwide. Some argue that the rise of egalitarianism (equality in the community) and, to a lesser extent, the decline of individualism (self reliance, independence), explain the rise of environmental opinions in recent decades.

The first important finding was that consistency between the content of messages and a person's prior beliefs has a substantial impact. But the message source had no effect on peoples' confidence people in the scientific reports: liberals have overwhelming confidence in the claim that offshore oil drilling is riskier than previously thought, irrespective of the source, and conservatives place more faith in the message that oil drilling is safer.

Given that liberals are generally pro-environment and conservatives are generally pro-development, this is exactly what the content hypothesis would predict: the ideology and the content of the message interact.

"One finding immediately jumps out. Californians generally have more confidence in expert claims that offshore oil drilling is riskier than previously thought than they have in claims that it is safer. Fifty-eight percent of the respondents express a great deal or moderate amount of confidence in expert claims that offshore oil drilling is riskier than previously thought," says Smith. Together, these findings raise the question of whether scientific studies are likely to have much impact on the public's views of the safety of energy sources.

The weighting towards claims that drilling is higher risk work in favour of environmental groups, giving them a substantial advantage in credibility, at least among the Californians in this study. Environmentalists most commonly warn about risks. "So if other claims by environmentalists are regarded with similar confidence, environmental groups have a strong hand in political disputes over public policy," Smith says.

The message content hypothesis is important because it directly addresses problems in current politics: Scientists and government experts report research findings, which policy makers dispute and sometimes vote as 'false' or 'junk science'. Charges of junk science have come from many groups, both left and right, and have been directed at scientific findings in many areas -- climate change, nuclear power, nuclear waste storage, genetic engineering, high-power electric transmission lines, pesticides, and oil drilling.

The findings are consistent with previous research showing that core values and prior beliefs influence whether people accept persuasive messages. But this is the first time the researchers are aware of to show that core values and prior beliefs have independent effects.

If researchers can replicate these findings in other policy areas, the influence of science on public policy debates will be in doubt.