The Sensibilities of Sensitivity and Specificity

The recent odious twitter spat between the self-appointed witchfinder Dr Dominic Pimenta and the aggressive broadcaster Julia Hartley-Brewer about covid false positive rates triggered by Hatt Mancock’s assertion that the rate was ‘less than 1%’ has yet again highlighted the rampant confusion that continues to plague the meaning and interpretation of screening and diagnostic tests. Dr No understands this confusion only too well, since he has struggled for many a long hour to get his head round what the test results and their derivatives — the sensitivity and specificity, positive and negative predictive value etc — really mean. So, in the interests of clearing his own head, and, he hopes, helping a few readers to clear their heads, Dr No is going to do a run through on tests, and explain what matters, and why it matters. Inevitably it is a long post, but at the end we do at least have something of a possible, but baffling, answer to the Pimenta Hartley-Brewer spat.

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Where Are We Now

This remarkable photo, apparently first published by The Spectator, begs a thousand captions, none of them polite. In the interests of least offence, Dr No suggests, ‘When I say jump, you jump!’, but really it almost works better without a caption, because it is the expression on the faces, and the fist about to thump the table, that tell the story. Cummings looks as if he has just been shot in the back with a poison dart, and is about to fall face down on the table, Boris looks like a truculent schoolboy, up before the head after being caught having yet another dump in the College rose garden (‘I couldn’t help it, sir, I had to go’), and Mancock looks like the truculent schoolboy’s hanger-on, who knows he too will get flogged, on a charge of common purpose. Or maybe he’s wondering whether the head knows about the spliff he had behind the College bike shed. But whatever the words and thoughts at play as the photo was taken, surely the most remarkable thing is the insight we gain of the disarray at the heart of government.

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Whackamolean Epidemiology

Listening to the Prime Minister’s speeches on the radio, one hears irregular thuds in the background, as if a workman in a distant room was testing the heft of a sledgehammer. The thuds are in fact the Prime Minister thumping the desk, dispatch box, or lectern, a displacement activity occasioned by his spectacular inability to hit a single covid nail on the head, let alone whack even a solitary virus. One fears the thuds will become louder and more frequent as time goes by, and start to drown out the words, until one day all speeches come to be the cacophony of a multitude of workmen beating a devil’s tattoos with their hammers as they demolish the stony guardians of ancient British liberties one by one, until we become, as Mainwaring almost said, a nation of automatons led by a lunatic who looks like a clown.

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The Pillars of Testing

Proof, were proof needed, that many of the pillar 2 community covid-19 tests done recently were carried out on asymptomatic people came yesterday morning from Absolutely Mancock. Absolutely doing the morning’s media interview round, he confirmed that as many as a quarter of the tests were done on people who absolutely were not eligible because they absolutely did not have either symptoms, or what he sinisterly called a direction from an official, to have a test. The rest of us have absolutely known about this problem for a while (in Dr No’s case, for weeks, if not months), and the problem it causes, which is once again to pour mud on the question of when is a case not a case. True false positives (positive result when no viral fragments are present) aside, much of the problem has to do with fact that the PCR (swab, antigen) test checks not for the presence of disease, or even entire infectious virus, but instead looks for tiny fragments of genetic material from the virus.

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Humans Are Biohazards

The title of this post is part of a quote from the CEO of a high tech company, thrilled by the opportunities covid–19 will provide for companies like hers to advance their prospects. The full quote, in this excellent article by Naomi Klein, is “There has been a distinct warming up to human-less, contactless technology. Humans are biohazards, machines are not.” Klein’s core point is that high tech has been waiting in the wings for a global event that will tip the scales in favour of mass adoption of human-less contactless technology across the board, and what better to bring about the tipping of the scales than a viral pandemic, which through its doctrines of social distancing, shelter-in-place (so American a phrase) and mandatory mask wearing constantly tells us that humans are biohazards. How perfect an opportunity for high tech to step forward, human-less, contactless technology at the ready.

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2020 Tin Foil Hats

Is wearing a facemask against covid-19 a curious, curious in that the intent is to keep the danger in rather than out, variant of the tin foil hat? Both are designed to keep an invisible peril at bay, and although neither has one jot of direct evidence that they work, wearers of both can point to studies done in physics labs that support their use, at least indirectly, though not without blowback. Advocates of both are fanatic in their zeal, brook no counter-argument, and fervently deny they patently look silly. The more Dr No considers it, the harder he finds it to distinguish between what now increasingly looks like two variations on a common theme, with the possible exception that by and large tin foil hat wearers don’t beat up non-wearers. Perhaps there are other novel tin foil hats that have emerged for the novel coronavirus? Well yes, there are. But we are only going to consider one, because it is a tin foil hat large enough to be a flying saucer. It is of course the lockdown. Unlike normal tin foil hats, this one isn’t just useless, it’s downright dangerous.

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Darzi Tests

Disclaimer: Dr No wishes it to be known that in no way does he condone calling the well intentioned but flawed Darzi tests Stasi tests. Any attempt to do so is very clearly a mendacious attempt to discredit a Noble Lord and his well intentioned but flawed  tests, and cannot be permitted under any circumstances. Should any such typo appear in this post, having escaped rigorous proof reading, Dr No makes his fullest apologies, begs forgiveness, and wishes it to be abundantly clear that any instance of Stasi test should of course always be read to mean Darzi test. No such reservations, however, apply to any suggestion that the tests are only fit to be disposed of, preferably with the aid of several litres of fast running water (hereinafter ‘the Khazi tests’).

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Just Another Seasonal Flu Like Illness

For some time, Dr No has been moving, or perhaps driven, to a determination — he uses the word with at least two of its meanings — that the only sensible considered response to covid–19 is to treat it as just another seasonal flu like illness. He knows full well that some will be of like mind, but that many — they know who they are — will react violently, in some cases with extreme violence, to any such suggestion. Dr No is a heretic! Burning at the stake is too lenient a punishment for heresy! Let him be hung, drawn and quartered, and his eviscerated staked body be displayed as a grim reminder to those who contemplate such heinous heresy! So it behoves Dr No to explain how he came to this determination.

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Multiphase Turbulent Gas Clouds

So incensed was Dr No on coming across a nonsense paper in the BMJ yesterday that he uncharacteristically dashed off a tweet denouncing the paper as ‘more nonsense from the milk curdler‘. The trouble with twitter — and the reason Dr No generally avoids it for primary communications — is that a tweet is limited, to 280 characters to be precise, and one image, and so almost always bars reasoned argument. If reasoned argument is akin to steady breathing, then a tweet is akin to a multiphase turbulent gas cloud, as sneezes are now known among the cognoscenti. Such esoteric language leaves one wondering whether the humble naked fart is also a multiphase turbulent gas cloud among the cognoscenti — it seems entirely possible, along with the silent but deadly multiphase turbulent gas cloud — but for today’s purposes we shall adopt the Yorshire way, and call a sneeze a sneeze, for it is the study of sneezes that is the bedrock — or rather quicksand — that underlies the nonsense paper.

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Surveillance Capitalism

If listening to Martha Kearney on the Today programme is like watching the mould grow on your breakfast yoghurt, then hearing Hatt Mancock’s hosannas for mass covid testing on an industrial scale on the same programme last week was enough to cause Dr No’s yoghurt pot to explode, with deleterious consequences for the immediate environment. Maybe, but only maybe because there are significant  unanswered conduct, consent and compulsion questions, the epidemiologist (lower case e) in Dr No can see the attraction, but the Individual (upper case I) in Dr No countered and then drowned the appeal by screaming privacy, Privacy, PRIVACY! Why? Because, while the surveillance programme might have a faint blue NHS logo tacked loosely somewhere on the threshold, the machinery inside is almost entirely privatised.

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