It’s journal club time (episode 391)! Lewandowsky et al. on scientific consensus

Thanks to the many friends who sent me emails, made late night phone calls, or showed up at my front door (during the time when the storm had knocked out internet & phone service) to make sure I saw Lewandowsky, Gignac, & Vaughan’s The pivotal role of perceived scientific consensus in acceptance of science in Nature Climate Change. It’s a really cool paper!

LGV present observational and experimental evidence relating to public perceptions of scientific consensus on climate change and other issues. CCP did a study on scientific consensus a couple yrs ago,  — Kahan, D.M., Jenkins-Smith, H. & Braman, D. Cultural Cognition of Scientific Consensus. J. Risk Res. 14, 147-174 (2011)–which is one of the reasons my friends wanted to be sure I saw this one.

The paper presents two basic findings. I’ll say something about each one.

Finding 1: Perceptions of scientific consensus determine public beliefs about climate change–and in essentially the same way that they determine it on other risk issues.

In the observational study, the respondents (200 individuals who were solicted to participate in person in downtown Perth, Australia) indicated their beliefs about (a) the link between human COemissions and climate change (anthropogenic global warming or “AGW”), (b) the link between the HIV virus and AIDS, and (c) the link between smoking and lung cancer.  The respondents also estimated the degree to which scientists believed in such links. LGV then fit a structural equation model to the data and found that a single “latent” factor — perception of scientific consensus with respect to the link in question — explained the respondents’ beliefs, and “fit” the data better than models that posited independent relationships between respondents’ beliefs and their perceptions of scientific consensus on these matters. So basically, people believe what they think experts believe about all these risks.

Surprised? “Of course not. That’s obvious!”

Shame on you, if that is how you reacted. It would have been just as “obvious!” I think, if they had found that perceptions of scientific consensus didn’t explain variance in perceptions of beliefs in AGW, or that such perceptions bear a relationship to AGW distinct from the ones on other risks. That’s because lots of people believe that skepticism about climate change is associated with unwillingness to trust or believe scientists. If that were true, then then the difference between skeptics and believers wouldn’t be explained by what they think scientific consensus is; it would be explained by their willing to defer to that consensus.

Most social science consists in deciding between competing plausible conjectures. In the case of climate change conflict, two plausible conjectures are (1) that people are divided on the authority of science and (2) that people agree on the authority of science but disagree about what science is saying on climate change. LGV furnish more evidence more supportive of (2) than (1). (BTW, if you are curious about how divided Australians are on climate change, check this out.)

In that regard, moreover, their finding is exactly in line with the CCP one. Using a large (N = 1500) nationally representative sample of US adults, we measured perceptions of scientific consensus on climate change, nuclear power risks, and gun control.  These are highly contentious issues, on which American citizens are culturally divided. Nevertheless, we found that no cultural group perceives that the view that is predominant among its own members is contrary to scientific consensus. (We also found that all the groups were as likely to be mistaken as correct about scientific consensus across the run of issues, at least if we treated the “expert national consensus reports” of the National Academy of Sciences as the the authority on what that consensus is.)

So next time you hear someone saying “climate skeptics are anti-science,” “the climate change controversy reflects the diminishing authority of/trust in scientists” etc., say “oh, really? What’s your evidence for that? And how does it relate to the LGV and CCP studies?”

Finding no. 2: When advised that there is overwhelming scientific consensus in favor of AGW, people are more likely to believe in AGW — and this goes for “individualists,” just like everyone else.

The experiment subjects (100 individuals also solicited to participate in person in Perth, Australia) indicated their AGW beliefs after being randomly assigned to one of two conditions: a “consensus information” group, which was advised by the experimenters that there is overwhelming scientific consensus (97%) on AGW; and a “no information” group, which was not supplied any information on the state of scientific opinion.

LGV found, first, that subjects in the consensus-information group were more likely to express belief in AGW. This result adds even more weight to the surmise that popular division over climate change rests not on a division over the authority or credibility of scientists but on a division over perceptions of scientific consensus.

Second, LGV found that the impact of consensus-information exposure had a stronger effect on subjects as their scores on a “free-market individualism” worldview measure increased. In other words, relative to their counterparts in the no-information condition, subjects who scored high in “individualism” were particularly likely to form a stronger belief in AGW when exposed to scientific-consensus information.

Although also perfectly plausible, this finding should definitely raise informed eyebrows.

Public opinion on climate change in  Australia, as in the US, is culturally divided.  Consistent with other studies, LGV found that individualism generally predicted skepticism about AGW.

We know (in the sense of “believe provisionally, based on the best available evidence and subject to any valid contrary evidence that might in the future be adduced”; that’s all one can ever mean by “know” if one actually gets the logic of scientific discovery) that individualist skepticism toward AGW is not based on skepticism toward the authority of science. Both the observational component of the LGV study and the earlier CCP study support the view that individualists are skeptical because they aren’t convinced that there is a scientific consensus on AGW.

Well, why? What explains cultural division over perceptions of scientific consensus?

One conjecture — let’s call it “cultural information skew” or the CIS — would be that individualists and communitarians (i.e., non-individualists) are exposed to different sources of information, and the information the former receives represents scientific consensus to be lower than does the information the latter receives.

But another conjecture — call it “culturally biased assimilation” or CBA — would be that individualists and communitarians are culturally predisposed to credit evidence of scientific consensus selectively in patterns that fit their predisposition to form and maintain beliefs consistent with the ones that prevail within their cultural groups. CBA doesn’t imply that individualists and communitarians are necessarily getting the same information. But it would predict disagreement on what consensus is even when people with those predispositoins are supplied with the same evidence.

CBA is one of the mechanisms comprised by cultural cogniton.

The same CCP study on scientific consensus furnished experimental evidence supportive of CBA. When subjects were asked to assess whether a scientist (one with elite credentials) was an “expert”– one whose views should be afforded weight — subjects tended to say “yes” or “no” depending on whether the featured scientist was depicted as espousing the position consistent with or opposed to the one that predominated among people who shared the subjects’ values.

In other words, subjects recognized the positions of elite scientists as evidence of what “experts” believe selectively, in patterns that fit their cultural predispositions on the risk issues (climate change, nuclear power, and gun control) in question. If this is how people outside the lab treat evidence of what “expert consensus” is, they can be expected to end up culturally divided even when they are exposed to the very same evidence.

At least one more research team has made a comparable finding. Adam Corner, Lorraine Whitmarsh, &  Dimitrios Xenias published an excellent paper a few months ago in Climatic Change that showed that subjects displayed biased assimilation with respect to claims made in newspaper editorials, crediting or discrediting them depending on whether the claims they made were consistent with what the subjects already believed about AGW. That’s not culturally biased assimilation necessarily but the upshot is the same:  one can’t expect to generate public consensus simply by bombarding people with “more information” on scientific consensus.

The LGV finding, though, appears inconsistent with biased assimilation, cultural or otherwise. The subjects in the consensus-information group were being supplied with evidence — in the form of information provided by experimenters — that suggested scientific consensus on AGW is very high (higher, apparently, than even subjects who believe in AGW tend to think).

The CBA prediction would be that more individualistic subjects would simply dismiss such evidence as non-credible — in the same way that subjects in the CCP study rejected the credibility of scientists who furnished them with information contrary to their cultural predispositions. Having been given no credible information in support of revising their assessment of scientific consensus, LGV’s individualist subjects would not (under the CBA view) be expected to revise their assessments of AGW.

But apparently they did! That’s a result more in keeping with the “information skew” (CIS) account of why individualists disagree with communitarians.  So it turns out after all that all we need to do is un-skew things. As LGV put it, their study “underscores the vital role of highlighting a scientific consensus when communicating scientific facts,” particularly when the underlying issues are “difficult to grasp or are hotly debated or challenge people’s world views.”

So do I “accept” LGV as evidence against CBA, and as evidence for being less skeptical about a communication strategy that focuses on simply “highlighting scientific consensus”?  For sure!

But I don’t see the evidence as super strong — and certainly not strong enough to change my mind on these matters given the sum total of the evidence, including but not limited to the previous CCP & Corner et al. studies. In Bayesian terms, I give LGV a likelihood ratio of 0.77 in favor of CBA (or 1.3 in favor of the alternative, CIS hypothesis).

The reason I am not inclined to assign more decisive weight to the LGV finding is that I’m not convinced that people in the real world will be nearly so willing to accept real-world information on scientific consensus as the LGV study apparently were to accept the LGV experimenters’ representations.

If individualists in the real world were that receptive to information “highlighting” scientific consensus, I’m very confident they would have gotten the message by now. You really have to be off the grid — off the planet, even — not to have heard over & over & over that there is “overwhelming scientific consensus” on AGW. One either accepts that information when it is presented — on tv, in newspapers, by people one talks to on the street corner — or one just doesn’t. And obviously a good segment of the population just doesn’t.

Basically, I’m taking the fact that “some people credit reports of scientific consensus on AGW yet many don’t” as the starting point for investigation, and trying to figure out who sees what & why. Again, the CCP experimental result is evidence, in my view, that people are motivated to selectively credit or dismiss evidence of scientific consensus in ways that fit their cultural prepositions (CBA).

Now in fact, I am surprised that individualistic subjects in the LGV study apparently did put so much confidence in the word of the experimenters. But that they did makes me question whether the situation those subjects were in is really comparable to one of people who are engaging real-world information sources.

I’m inclined to say that in this regard I think the CCP experiment was more realistic. We — the experimenters — made no representations to our subjects about the state of scientific consensus. Rather, we showed them some evidence — a scientist taking a position — and let them decide for themselves what weight to attach to it. They told us that they viewed what we were showing them as valid evidence of “what experts believe” only when that evidence was consistent with the position that predominated in their group.

I think that’s closer to the situation that we can anticipate people will be in outside the lab when real-world people — from journalists to advocates to individual scientists to their fellow citizens — try to “highlight” AGW consensus to them. The expectation that people in that setting will be dismissive toward representations that challenge their predispositions is strongly supported by Corner, Whitmarsh, & Xenias (2012) as well.

Actually, LGV come pretty darn close to saying they agree with this point. They write:

At first glance, our results challenge the results of Kahan and colleagues, that perceived consensus operates like any other fact that is equally subject to dismissal as other evidence surrounding AGW. However, on closer inspection, the study by Kahan did not provide socially-normative information about a consensus (that is, ‘97 out of 100’) but instead presented participants with an informational vignette, attributed to a fictional expert, that either described the risk from climate change or downplayed it. Because this manipulation provided anecdotal rather than social-norming information, it is not surprising that participants rated the source as less trustworthy if the message was worldview dissonant. Normative information, by contrast, is widely assumed to be more resilient to ideologically-motivated dismissal ….

Right: if one provides information that people view as “socially normative” — i.e., as worthy of being believed —  they’ll accept it. But the issue is how to make people view that information as “socially normative” when it is contrary to their cultural predispositions? I just find it implausible to believe that people in the world are as open to real-world evidence (including media accounts & the like) purporting to tell them that they & all their peers are wrong about scientific consensus on AGW as the subjects in the LGV experiment apparently were when the experimenters told them  “97 out of 100 climate scientists believe in AGW.”

My skepticism, however, is not a reason for anyone, including me, to dismiss the significance of LGV’s experimental finding.  Only a person who doesn’t really understand how empirical study enlarges knowledge would think that one can find a study compelling, insightful, and challenging only if one is “convinced” by the conclusion.

Indeed, if you get how empirical inquiry works, then you’ll know how I or LGV or anyone else should respond to the questions I’ve raised: not by putting this paper aside, but by getting a firm grip on it & trying to reciprocate its contribution to knowledge by doing additional studies that take aim at exactly what is giving me pause here.

E.g., if one embedded the statement “97 out of 100 scientists accept AGW” in a NY Times newspaper story, would individualists react the same way as the ones in this study did? Would they be just as likely to believe that representation as they would be to accept the representation that “only 3” — or more plausibly for experimental purposes, “only 43” or “only 47”–“of 100” scientists believe in AGW? Would egalitarian communitarian subjects likewise credit just as readily either representation on the state of consensus on AGW? Same for safety of nuclear power?

Show me that — a result that essentially replicates LGV in a in the Corner, Whitmarsh, & Xenias (2012) design — & I’ll definitely be revising my priors on CBA by a humongous amount!

But I won’t have to wait for that result (or the opposite of it) to get the benefits of both knowing more and having more to puzzle over as a result of this paper.

I think it’s cool! Read it & tell me what you think!


Corner, A., Whitmarsh, L. & Xenias, D. Uncertainty, scepticism and attitudes towards climate change: biased assimilation and attitude polarisation. Climatic Change (2012), on-line advance publication at

Kahan, D.M., Jenkins-Smith, H. & Braman, D. Cultural Cognition of Scientific Consensus. J. Risk Res. 14, 147-174 (2011)

Lewandowsky, S., Gignac, G.E. & Vaughan, S. The pivotal role of perceived scientific consensus in acceptance of science. Nature Climate Change (2012).

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