Sep 30 2008

Scientific Consensus

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I often refer to the “consensus of scientific opinion” and was asked to elaborate on exactly what that is and, more importantly, how it is determined. From a practical point of view, how can the average citizen get a handle on what the scientific consensus is on any given topic? For some burning questions, like whether or not there is significant anthropogenic global warming, much of the debate centers around whether or not there is a consensus and what it means. For others, like should we invest in biofuel from corn, a consensus seems elusive.

The Role of Consensus

For anyone trying to take a scientific approach to knowledge about the world, we must rely heavily upon experts, or those who are more knowledgable than we are. There is no choice – there is simply too much specialized scientific knowledge for anyone to be an expert in everything, or even a significant portion of scientific disciplines.

Further, being an educated layperson is usually not enough to form your own opinions on specific scientific questions. Forming a reliable opinion often requires a level of detailed knowledge that only an expert in the field can obtain. Even experts can be wrong, of course, and since lay opinions are likely to span all possibilities, some are bound to be correct. Experts, however, are far more likely to have an opinion that accurately reflects the evidence and to understand how to incorporate new evidence as it comes in.

There are plenty of examples, however, of experts coming to conclusions that were profoundly wrong. How is the public supposed to rely upon expert opinion, then? Proper scientific authority does not rely in any individual. Individuals are quirky and may have biases and influences that lead them astray.

Scientific authority, rather, lies in the consensus of scientific opinion. When many experts look at the data and come to the same conclusion, it is more likely to be accurate than anomalous. A consensus of many experts is simply more reliable than the quirky opinions of a single expert.

It is therefore the consensus of opinion (or should be) that determines what goes in the science textbooks, what is taught is science classrooms, how applied sciences are regulated, and how society spends its resources.

When Consensus is Wrong

There are, of course, examples of when the scientific consensus proved to be wrong.  In fact, this happens all the time – whenever evidence points in one direct but later evidence reveals a different answer or (more likely) reveals a deeper reality. It is the nature of science that is constantly changes in response to new evidence, and so the consensus of opinion is a moving target.

But not all scientific consensus is created equal.

We therefore need another assessment in addition to what the consensus is on a given question – we also need to consider how solid the consensus is. There are some question for which the scientific consensus is so solid (reflecting an overwhelming amount of evidence) that it would be perversely absurd to deny it. The earth is an oblate spheroid. DNA is the molecule that carries hereditary information. Life on earth is the result of common descent. Infectious illnesses are caused by microscopic organisms.

Other conclusions are solid but not beyond the possibility of revision. Still others are probable but preliminary. And some scientific questions are genuine controversies, without a clear consensus. The more solid a consensus is, the less likely it is to be overturned in the future. It’s not impossible for a consensus to be overturned – it’s just progressively unlikely as the consensus becomes more solid.

When is a consensus of scientific opinion not reliable? If the scientific process is working properly, then never. So the real question is, when does the scientific process break down. Here are what I think are the read flags for a supposed consensus of which you should be skeptical:

– The consensus seems premature.  If we have only been studying a problem for a short time, the overall amount of evidence is small, or there has not been time for proper replication of experiments to occur, then scientific opinions are likely premature.

– If the consensus emerges from a highly politically or ideologically charged atmosphere.

– If the consensus exists only within a subculture, such as a fringe group looking to promote a predetermined conclusoin.

– If the consensus is dominated by industry self-interest.

As I said – these situations do not represent genuine scientific consensus, but rather a breakdown in the system or an ideologically or otherwise motivated subgroup looking to masquerade as a scientific consensus.

So What Is The Consensus

With all this in mind, how can the average person go about figuring out what the consensus is on any scientific question and how solid it is? A good place to start is to see if any relevant institution has put together an expert panel to review the evidence and make a consensus statement. If the American Academy of Neurology puts out a position paper on a neurological issue, it probably is a good reflection of the consensus.

Of course, panel decisions are only as good as the panel. You have to ask whether or not the panel was representative and objective. When Clinton put together a presidents panel on alternative medicine and packed it with alternative medicine providers, that is not exactly what I would consider a reflection of the scientific consensus. If you cherry pick the opinions you choose – that skews the results, and does not reflect the true consensus.

Also, for a consensus numbers matter (by definition). You can always find experts to support any belief – but what do most scientists think? Surveys (when well done) are useful for this purpose. Over 98% of scientists accept the fact that life on earth is the product of organic evolution and displays features of common descent. That is an overwhelming consensus that has endured for decades.

Percentages are more important that absolute numbers. Creationists try to bamboozle the public by trotting out as many creationist scientists as they can – distracting from the more important fact that >98% of scientists disagree with them.

Another good source of information is systematic reviews of the literature. This is a mechanism that experts use to develop their consensus, in fact. If multiple independent reviews all come to the same conclusion, that is a good indication of the consensus.

For politically controversial topics the process of determining the consensus can be challenging. This is because ideological groups have discovered how to best muddy the waters to obscure the consensus. Many have formed their own institutes (like the Discovery Institute for Intelligent Design) with the specific purpose of creating the impression of a scientific controversy where none exists.

Industry has discovered that they can pollute the scientific literature by funding poorly designed studies designed to produce a favorable outcome. Ideologically aligned organizations have formed to fund research to promote their agenda.

The worst manifestation of distorting the process are groups like antivaccinationists who have used bully tactics and intimidation to attack scientists who disagree with their agenda, or simply when they don’t like the outcome of their research.


The institutions of science are still strong and for most questions it is not difficult to find a reliable reflection of the consensus of scientific opinion, once you know what to look for. For most questions it is simply a matter of looking for statements put out by institutions or reviewing a broad cross-section of the scientific community, and not putting much weight on the opinions of a lone scientist – no matter what their credentials.

But the institutions of science can also be very precarious. There are actually many systematic attacks on the institutions and practice of science from a variety of directions – but generally from those with an ideological axe to grind. There is no shortage of well-funded groups looking to distort the process of science, and therefore the impression of consensus, to rig the game in their favor, or ensure a favorable outcome. Short of that they wish to muddy the waters – to at least sow confusion to keep as many people from understanding the scientific consensus as possible.

For this reason science needs constant defense and support, and ideological groups distorting science need watchdogs.

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