Prior Plausibility: How to First Assess Claims

A necessary tool in the scepticism kit is prior plausibility (or probability). I’ve mentioned it before, but not sure I’ve explained it well. It’s a good starting tool for consumers to be protected from scams, fads, influencers, nonsense etc.

The term is a shortcut to forming a quick estimation of the truth of a claim. It must be used correctly, of course and in good faith. Importantly, it is linked directly to ‘what we already know to be true’. It’s how I am often able to confidently dismiss or be sceptical of a claim without first digging far into it.

Prior plausibility in science is not just a guess. It’s informed by the existing body of scientific knowledge – the well-established and high confidence stuff, primarily. From there, if the claim passes the lowest bars of plausibility, then it may indicate there’s something worth checking out; providing there are no further serious reasons to doubt the claim.

Prior plausibility can often be the difference between outright dismissal and provisional acceptance of a claim. The dismissal can also be provisional – pending compelling evidence of course. Similarly, the acceptance can be tentative, not something you’d put money down on but something you’re not yet willing to rule out completely. Again, this is subject to further compelling evidence being found.

I’ll now use several examples where different levels of prior plausibility can be used to make a shortcut judgment of various claims, explaining why you can have such levels of confidence in rejecting certain ones outright. This dismissal can often appear arrogant and ‘superior’ to those who do not understand why the claims are not plausible; those who do not exercise prior plausibility.

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Low Prior Plausibility 

Alien Visitation

Aliens visiting Earth is an example of a claim which has extremely low plausibility, given the vast knowledge we have about physics and the universe, when compared to the excruciatingly poor ‘evidence’ people making that claim refer to. The prior plausibility of this claim is close to zero, and as such this is one which would come into the ‘dismiss outright’ category, pending actual evidence. An understanding of what qualifies as evidence is also necessary.

Any claim for which there are many more reasons to think it is wrong than right has an inherently lower plausibility of being right, than of being wrong. Take this excerpt of a brilliant article I will link later:

“To give a silly example, imagine someone tells me that pouring Mountain Dew into my car’s engine will improve its performance. Even without actually testing that hypothesis, I can reject it with a very high degree of confidence. I know enough about how cars work to know that it is almost certainly wrong. In other words, this idea conflicts with what we already know about how cars work, therefore it has a very low prior probability, and there’s really no good reason to bother testing it. Further, ignoring this suggestion that Mt Dew is good for cars isn’t being “close-minded,” “ideological,” or “dismissive.” There’s simply no good reason to think that it is right and plenty of good reasons to think that it is wrong. Science inherently has to use what we already know as a starting point, and throwing everything that we know out the window to chase absurd suggestions is a substantial waste of time and money.”

Herbs, Supplements, Remedies

Another common example of low plausibility of any benefit are any marketed herb or remedy – Ashwagandha, Ginkgo Biloba, Echinacea, Milk Thistle [2], Elderberry, CBD, Turmeric, activated charcoal (makes your food less nutritious), ‘Superfoods’ [2], Cranberry [2], Coffee Enemas, and hundreds more. What’s more – they can mostly do more harm than good, something drugs are developed not to do.

Every single time you see a ‘new’ one, you can be pretty sure that most of what underlies the marketing is empty space, and 999 times out of 1000 you can rest easy that these sellers are doing everything they can to appear science-backed, to sell their product. The big picture about these things is that if there was a clinically useful active ingredient in them, they would be isolated and made better, into a drug – as the ones that do have a useful ingredient have been (Aspirin and Penicillin for example, both derived from natural sources). At the stage they can be said to have a demonstrably true, useful effect, they should then be regulated as drugs, which they would become.

The overwhelming majority of them are unproven or proven to be useless – therefore offering little plausibility the next time a marketed remedy is pushed onto your feed, that it’s any better. Knowing this will save you money, false hope, and from being fooled.

I’m giving a shoutout here to mushroom based ‘energy’ powders and brain ‘boosters’, and nootropics. They’re currently one of the newer big marketing ploys out there and carry a new set of claims with no supporting evidence.

Detoxes, Juice Cleanses

Detoxes and juice cleanses are another good example of having no plausibility. It’s no use saying, ‘but what about THIS new detox, with ‘x’ ingredient in it, backed by ‘y’ doctor or influencer?’. The thing that gives detoxes next to zero plausibility is nothing to do with the ingredients or what perceived credible ‘doctor’ or ‘scientist’ is touting it. This is because detoxes as a concept in biology can not ‘work’. They have no biological plausibility at all – as the scientific consensus frequently points out.

The body has its own measures in place to get rid of toxins – the kidneys and liver. Beyond that, you can’t further ‘detox’ or ‘cleanse’ by using something else. Therefore, any marketed product that follows this claim is already invalid – and will almost certainly have no compelling evidence to support it.

Perpetual Motion/Free Energy Generators

Claims emerge from time to time about generating free energy – self-sustaining systems which allegedly would mean you never had to refuel your car, for example. There was one that went viral in 2020 where it was claimed that attaching a generator to car wheels would generate electricity which would then be stored and reused to power the car, meaning that it would never run out of electricity.

This claim and any like it, have no plausibility and are instantly dismissible if you are aware of one simple but solid physical fact: the laws of thermodynamics (a ‘law’ in science is a highly tested, true and predictive attribute of the universe which we have the highest confidence in, and has stood the test of every bit of scrutiny).

The short version of these physical laws, aka reality, is that it is completely impossible for a perpetual motion or free energy device to work, by several measures of reality. Therefore, we need not entertain the idea. Isn’t it more fascinating anyway, the very fact that this is impossible?

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High Prior Plausibility

Vaccines

Now let’s pivot to an example of high prior plausibility. Vaccines are among the most effective preventative measures in medicine. Vaccines have saved more human lives than any other medical invention in history.

They are also the most highly tested and scrutinised and safest intervention we have. Now, given that we have a long track record of their safety and effectiveness vs the low (if not the lowest) risk in all of medicine, combined with other factors, like the complete backing of the scientific literature, consensus, and scientific and public health institutions, plus the fact that we have literally eradicated many diseases which used to kill and injure at high rates, gives vaccines as a concept very high prior plausibility. Specifically, a scientific or public health institution making a claim of a newly made vaccine (which will have all necessary testing in place in years before), needs next to no scepticism that it would work conceptually – it’s very likely true.

So, given our vast knowledge and success with vaccines, we know they have very high prior plausibility. The claim checks out historically, and so you should have little problem believing it at face value – although while still doing the necessary checks for its advocacy among multiple scientific sources.

Fluoride for Dental Health

Frequently fearmongered about by conspiracists, fluoride is the most demonstrably effective substance for protecting and prolonging dental health, concluded from data gathered over more than 100 years. So much so, that it’s the only consistent ingredient recommended by dental health professionals globally, and they advocate its use across all toothpastes and mouth washes.

Not only does it work in dental care products, but it also shows reduction in tooth decay and overall oral health when introduced to drinking water in areas of poverty. There’s mountains of data to back it up, and to prove its safety – the levels used in products and in the water supply are much lower than the safety limit for human consumption. Yet, it still proves effective for its purpose (this is one distinction from herbs and supplements, which are not regulated, but when they are taken down to safe and tested levels often lose any promising effect. This means they are too toxic to humans).

Therefore, a new dental care product with fluoride has very high prior plausibility, whereas one which claims to have the same protection but without fluoride, has low prior plausibility to be effective – because nothing else has come close to the effectiveness of fluoride.

Einstein’s Theory of Relativity – Spacetime Exists

Proven beyond doubt over and over again, the scientific theory of relativity is a complex, highly tested set of observations of the real universe that are true. They not only continue to pass the tests of criticisms thrown at it, but it predicts and solves physics and engineering problems that technologies rely on, and corrects for, such as GPS navigation. The gravitational distortion in location pinpointing was predicted by – and solved by – relativity, as the technology was developed, thus validating the accuracy of the theory.

Discoveries in recent years were still made, which were accurately predicted by relativity, and so this is up there in some of the most established and demonstrated scientific knowledge we have. This equals very high plausibility if a claim about the gravitational behaviour of interstellar objects is made within the correct framework of - and informed by - relativity.

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What informs prior plausibility?

A little knowledge always helps distinguish plausibility, but this isn’t readily available for a lot of people. Some understanding of scientific concepts and logic, critical thinking, etc., goes a long way. But there are still plenty of ways to make better decisions as an average consumer of information. I wrote a whole post about that if you are interested.

Judging prior plausibility requires a little knowledge of the topic, a little critical thinking, and a little understanding of what qualifies as evidence – and how to interpret it. It sometimes easier to have a bit of knowledge of things that are just wrong – not necessarily right (which is usually a tougher answer). Think of it like a jigsaw – you could test 50 pieces to fit another piece, knowing confidently that each one prior to the correct one was wrong. However, you might not know the right one yet. But this doesn’t stop you from identifying which pieces are wrong.

Above all, try to judge claims that spring up out of nowhere against as many scientific sources as possible. Where there is no criticism to be found, or no information at all other than touting a plethora of benefits, or anecdotes, it’s likely a red flag – low plausibility. If you don’t have enough information, then there’s no shame putting the claim on hold and sitting on the fence.

Here is a rough table which would inform the appropriate level of scepticism to apply to claims, based on their prior plausibility, much like I have done in the examples earlier.

Prior Plausibility (informed by science)	Level of Scepticism
Zero plausibility ·         Homeopathy ·         Reiki or other undetectable ‘energy’ ·         Free energy devices	Don’t waste another second! Dismissed!  Flies in the face of basic scientific facts, uses broken logic, invents nonsense and poorly defined, unproven or disproven, or untestable concepts.
Very low plausibility ·         Dubious/unstated mechanisms. ·         Conspiracy Theories without evidence. ·         Contradicts previous body of evidence.	Very high scepticism  Obvious red flags and contradictions of prior knowledge without backing it up.
Low plausibility ·         Claim is unproven but makes money. ·         More questions than answers. ·         Logical inconsistencies in reasoning.	High scepticism Insufficient evidence, patterns in reasoning or evidence similar to other debunked claims. Running with the hype before substantiation.
Difficult to tell but plausible ·         Small studies, case studies. ·         Not ‘impossible’ by current knowledge. ·         No immediately obvious contradictions. ·         Recognises limitations. ·         No hype/certainty. ·         Too much hype/certainty.	Be Sceptical Seek better info. Claims made without strong evidence have less merit than a 50/50 chance, because of the many ways we can be fooled or be wrong. Confirmation bias is rife in this category.
High plausibility ·         Consistent with prior scientific findings. ·         Criticisms/limitations addressed appropriately. ·         Passed preliminary testing and studying with positive results. ·         Claims are in line with the current evidence and don’t overshoot it.	Low scepticism  Still a relevant degree of it until sufficiently demonstrated. Tentative acceptance of the claim is ok, but low certainty.
Very high plausibility ·         Independently replicated among science institutes globally. ·         Larger effect than placebo. ·         Well-controlled and designed studies (double blind, randomised, large study).	Scepticism not very necessary  Subject to checks and verification. Provisional acceptance of the claim is safe.
Established, demonstrated scientific knowledge. ·         Scientific Theories (Evolution, Relativity) ·         Scientific Laws (thermodynamics) ·         High certainty. Predictive.	Zero scepticism required Highest bar of scrutiny passed. Scepticism would be wasted time, inappropriate and counter-productive. It would actually indicate insufficient understanding of the topic to be sceptical of a scientific consensus of evidence.

Although my above explanations are hopefully adequately simplified, a better, more comprehensive explanation can be found in the below embedded post – and click through into the full article. It’s written by a scientist, with an even greater understanding of the concept than me. Well worth the read:

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Conclusion

One of, if not the first thing that should be considered if you want to know the truth of a product or likelihood of a claim, is prior plausibility.

It’s a tool you can apply on a detailed level if you’re well-informed, or on a lay persons’ level with a bit of digging.  Time, effort and money is wasted all too often by consumers of information without the necessary checks in place, and the more gullible we are, the more at risk we are personally, and to those close to us – merely of being fooled, if nothing more serious.

If we are too quick to judge a claim as favourable, then we tend to skip the checks and incorporate it into our identity for the time being or our social standing. This makes it difficult, but never too late, to rewind and pause a second, check that we aren’t first deceiving ourselves. It’s much better to address it sooner, than to fall irreversibly deep into an idea and then have to back out.

I’m sure nobody likes to be perceived as gullible, much less likely be gullible. But that doesn't mean we should ignore it when it inevitably happens from time to time. In order to learn from these kinds of mistakes, we must be humble to ourselves, and acknowledge the error such that it can be recognised the next time.

Dismissing a claim with low prior plausibility and a healthy level of scepticism is not a cynical, killjoys’ game, ideological, or close-minded.

Dismissing a claim with low prior plausibility is retaining one’s own power, consumer protection, and a privilege we should practice and celebrate intellectually.

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