Evidence-based Life

“We must trust to nothing but facts: these are presented to us by nature and cannot deceive. We ought, in every instance, to submit our reasoning to the test of experiment, and never to search for truth but by the natural road of experiment and observation”
(Antoine Lavoisier, 1743-94).

“Nothing is too wonderful to be true, if it be consistent with the laws of nature”
(Michael Faraday, 1791-1867).

Evidence-based medicine was defined in an influential paper in the British Medical Journal 1996 as “The conscientious, explicit, and judicious use of current best evidence in making decisions about the care of individual patients.” It seems surprising that it even needed defining. How could sensible medicine not be evidence-based? The authors consider, and reject, the mutually contradictory arguments that, on the one hand, “All doctors do it anyway” and, on the other hand “It’s a dangerous innovation perpetrated to suppress the freedom of doctors to exercise their clinical judgement.” I want to generalise the arguments and advocate what I am calling Evidence-based Life.

Every moment of our lives we are faced with decisions. What shall I do next? What do I believe? To help us decide what to do next, we can draw upon copious evidence: the evidence of our senses, evidence from books, from conversations, newspapers, the Internet. We have the evidence from past experience (What happened when I previously was in this situation and did so-and-so?). We have evidence from a kind of future, as we simulate possible futures in imagination (I can see myself doing so-and-so and I can imagine the consequences). We can take advice from friends or mentors, books or traditional wisdom – and that can be seen as vicarious borrowing of other people’s past experience and simulated futures.

Much the same can be said of what we believe. I believe the world is round because I’ve flown to Australia via Asia and returned via America. I believe it because I’ve seen photographs from space. I believe it because of books I’ve read, lessons at school from teachers who seemed to know what they were talking about, and so on. I believe it because physics books tell me of a principle whereby large bodies tend to become spherical under the influence of gravity.  A very great deal of what we know, even that which really is based on sound scientific evidence, we have to take on trust, because we haven’t the time or the ability to examine it in detail.

Even expert scientists haven’t the time or the expertise to evaluate sciences other than their own. Most biologists are ill-equipped to understand modern physics. And vice versa although, I have to admit, to a lesser extent. In any case, nobody has the time to do full justice to all the detailed research papers in a journal such as Nature or Science, even if we could understand them. If we read a report that gravitational waves have been reliably detected as emanating from a collision between two distant galaxies, most of us take it on trust. It almost sounds like taking it on faith.  But it’s a faith that’s more securely grounded than, say, religious faith. That’s an understatement. When biologists like me express “faith” in the findings of physics, we know that physicists’ predictions have been verified by experimental measurements to find accuracy. Very different from “faith” in, for example, the doctrine of transubstantiation which makes no predictions at all, let alone testable and tested ones.

Nevertheless, scientific evidence is not always reliable. With the best will in the world, scientists can deceive themselves. Medical science has adopted the Double Blind Control Experiment, an admirable device for eliminating all possibility of subjective bias. Long ago, my then wife Marian (now a Fellow of the Royal Society) and I used it for fun in a trivial demonstration experiment. We wanted to know who made the best razor blades for shaving, Gillette or Wilkinson. Our quality criterion was how long a blade would last before I found it uncomfortable to shave and discarded it. Obviously that was a subjective judgement. It was important that I should not be allowed to know which make of blade I was using to shave. So Marian was solely responsible for putting a new blade into my razor, every time I pronounced the previous one worn out. If she had alternated the blades, Gillette, Wilkinson, Gillette, Wilkinson etc, that could have given me a clue. So she chose the blades according to a previously written-down random sequence, which I was not allowed to see. After a previously written-down number of blade-changes (I can’t remember what that number was but it had to be pre-determined), we looked at the data, consisting of a series of durations measured in days before each blade wore out. We analysed the data statistically and concluded that Wilkinson blades were significantly superior.

This was technically a Single-blind experiment. There remained the possibility that Marian could have inadvertently influenced my decision on when to declare a blade exhausted – the so-called Clever Hans Effect. A German horse called Clever Hans was apparently able to do simple arithmetic, tapping his hoof five times, say, when asked “What is two plus three?” It was eventually revealed that his trainer was unconsciously giving him cues, subtly changing his body language when Hans’s hoof taps reached the right number. Ideally our experiment should have been not Single Blind but Double Blind: the person inserting the blades into the razor should have been ignorant as to which was which – a little harder to arrange, though not impossible. Somebody else, neither Marian nor I, would have prepared a randomised sequence of blades, then Marian should have dispensed them when I pronounced the previous one spent. Clinical trials of new medicines nowadays usually follow the Double Blind design: the patients, the doctors or nurses administering the doses, and the experimenters judging the medicine’s effectiveness, and are kept in strict ignorance as to which patients get the drug, which they control. Without the strictures of the Double Blind design, there is always the danger of subjective judgement creeping in.

Blind control trials constitute only one weapon in science’s armoury against being misled by subjective judgement. Experiments are repeated. Scientific papers are rigorously refereed before publication and exposed to critical scrutiny afterwards. Experiment itself is the only ultimate safeguard against the notorious “correlation doesn’t have to imply causation” truism. Correlation really does imply causation if the putative cause happens when an experimenter makes it happen, rather than waiting for it to happen spontaneously. Of course, the experimenter must make it happen on a large number of independent occasions, and at random rather than in a regular pattern such as might introduce a spurious correlation. Finally, the correlation must be unlikely to have arisen by chance – unlikely according to some agreed criterion such as, “If we repeated the whole experiment a thousand times, we’d expect only one of those repeats to yield a result as extreme as this by chance.” That’s what tests of statistical significance are for.

In advocating evidence-based life, I don’t of course mean we should do double-blind, statistically-analysed experiments before making a decision, or before believing anything. Life’s too short, and there are many other reasons why it would be impractical. But it is worth imbibing the spirit of evidence-based medicine by being deliberately aware of possible sources of bias. Have I looked even-handedly at the available evidence or did I under-value or even ignore evidence that contradicted my prior beliefs? Or evidence that might have contradicted the beliefs of my tribe (religion, political party, favourite opinion-leader etc)? Do I read only the Guardian and ignore the Telegraph? Or vice versa. Do I watch only Fox News and ignore CNN? Do I tune out when exposed to news, or views, that contradict my prior prejudices?  Are my views on climate change (vaccination, Covid-protection masks) based on the best available evidence, or are they coloured by political or religious prejudice, or tribal loyalties of some kind?

Evidence-based Life could justify a whole book, not just a brief essay such as this. So let me just mention some of the more insidious and alluring alternatives which might tempt us away from evidence. I’ll list them in the form of headings to which I might return in future postings. 

It’s how I feel. It may not be true for you but it’s true for me.

Alternative “ways of knowing” are just as valid as science, which is just the mythology of a white male tribe.

I don’t need science, I’ve got my Holy Book.

I don’t need science, commonsense is good enough for me.

The evidence of my biology clearly indicates that I am male, but I feel I am a woman therefore I am a woman.

Richard Dawkins