It’s not an easy evaluation to pull off, “worse than Hitler”. It has proven impossible to match the extent of Hitler’s destructiveness. In the absence of that, to say that anyone – Donald Trump, as a wild for-instance – is worse becomes an insult to the memory of Hitler’s victims, since it asserts that the dictator’s nature and his efficiency can be separated, and his true singularity lay not in evil but in administrative prowess. But if you approach it a bit more systematically and show your workings, you can get round that – which is what an Oxford researcher, the psychologist Dr Kevin Dutton, has done.

Dutton has ranked world leaders throughout history on the Psychopathic Personality Inventory – Revised (PPI – Revised), and awarded Trump a score of 171, two points more than Hitler. There’s not much in it at that level, though it doesn’t assure their capacity for genocide – Henry VIII trumped both at 178. Hillary Clinton doesn’t fare brilliantly in the test, scoring 152; that’s between Napoleon and Nero.

There are 56 traits in the test, not all of them negative: social influence and fearlessness could go either way; even egocentricity has its uses. Cold-heartedness is harder to make a case for. Many of them are qualities that businessmen and women are admired for – ruthlessness, charisma, dishonesty, a lack of concern about the future. It has been a commonplace for years to note that psychopaths and highly successful people in business share a lot of characteristics. It is only relatively recently that this has become a field of academic inquiry – Joel Bakan, law professor at the University of British Columbia, and Jonathan Aldred, an economics fellow at Cambridge, have started to delve into the social effects of a corporate world that doesn’t just accept amorality but positively valorises it. None of them are positive, but we probably didn’t need the PPI to tell us that Donald Trump was not a force for good.

Obviously, Dutton didn’t conduct face-to-face interviews with the figures, and therefore contravenes the so-called Goldwater rule, a code of honour among psychiatrists whereby you don’t diagnose people, especially in public, who you have never met. (Only psychiatrists sign up to this; psychologists don’t, possibly with the defence that their diagnoses have less consequence – they couldn’t have you sectioned without a doctor, for instance.)

However, if we can turn a blind eye to that and pile in, with Trump I have always found the narcissism diagnosis more convincing. Simon Baron-Cohen, who developed the empathy quotient test, makes the distinction between cognitive empathy (you find it easy to intuit what other people are feeling) and affective empathy (you can’t guess what other people are feeling, but when you know, you feel it too). People with autism score very high on affective empathy and low on cognitive empathy, and people with psychopathy are the opposite; put simply, they can read people easily but don’t care about them. Donald Trump seems to lack any qualities of perceptiveness or insight that would allow him to read other people, even for nefarious purposes, and in that has the classic stamp of the high narcissist. Goldwater, schmoldwater.