Recently, David Friedman posted a response to an argument from Michael Huemer about when one should defer to experts or attempt to figure out the truth of some issue directly. David Friedman argued more in the direction of working out the truth directly, while Huemer seemed to argue more in favor of deferring to experts. There may be less disagreement between the two of them in principle than it seemed at first – in the comments, they both make some quick caveats and clarifications that seem to narrow the apparent gap in their views quite a bit.
Still, there’s one heuristic I think is worthwhile to add to this conversation. Sometimes, experts will disagree with each other, and we might ourselves not have the knowledge needed to properly evaluate which one is more likely to be correct. In those cases, what should we do?
For example, let’s say you wanted to know as much as possible about how to mitigate the effects of aging and to live longer. Right now, two of the biggest names in longevity research are Dr. David Sinclair, author of Lifespan, and Dr. Peter Attia, the author of Outlive. Let’s say I want to know how to best live a longer, healthier life. Both of these men are about as well-educated on this topic as anyone can be at this point, and their level of relevant knowledge vastly exceeds my own, so I read their books looking for advice. On the topic of how to eat, David Sinclair argues that it’s very important to limit the amount of protein in your diet. Meanwhile, Peter Attia argues that it’s very important to have a high protein diet – eating far more protein that the standard recommended daily allowance guidelines show.
Okay, so now we have two experts who offer contradictory advice. I’m in no way an expert in nutrition science, and I’m not likely to become one either. In this case, is there some heuristic I can use to decide which of them is more likely to be correct?
I believe there is, and in this case, it points me in favor of Peter Attia. When this kind of situation arises, my usual response is to lean towards the person who is making the more modest claim. David Sinclair’s claims are quite extravagant – the subtitle of his book is “Why We Age – And Why We Don’t Have To.” He argues that aging is optional and can be halted or even reversed – which is a very, very strong claim. Peter Attia, by contrast, makes the much more modest claim that we can slow the effects of aging, modestly increasing our lifespan and spend our last years healthier and with greater control of our faculties than we otherwise would. For example, in his own case, he doesn’t think it’s in the cards for him to live to 100, but he thinks that the dietary and lifestyle choices he recommends might help him live 8 to 10 years longer than he otherwise would have and will make his quality of life during his final decade much higher than it otherwise would be. This makes me far more inclined to assume that Peter Attia’s advice is correct.
This is basically operating in the spirit of Bayes Theorem about prior probabilities, and Carl Sagan’s dictum that extraordinary claims require extraordinary evidence. Almost by definition, an extraordinary claim just is a claim with a low prior probability. If two experts with vastly greater knowledge than me are arguing for opposing positions, and if the arguments and evidence they offer seem equally strong to me, then I rule in favor of the one that started with the more modest claim – that is, the claim that started out with a higher prior probability.
Is this a guarantee of accuracy? No, of course not – that’s why it’s just a heuristic. But I still think it’s a good tool, one that will point you in the right direction more often than not.
