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Left Shit


Posted by Dr No on 30 November 2012

blancmange.jpgThe title for this post arises because Dr No has idly been playing Shorter Titles, the I’m Sorry I haven’t A Clue game in which panellists are invited to submit film (or song) titles where a single letter omission changes the meaning – Oldfinger, The King’s Peech, Rear Widow, The Godfarter, The Tird Man, that sort of thing – but as Jack Dee would say, they don’t work in print - the original title here being Left Shift, the hypothetical statistical fancy much beloved of the medical Islingtonistas who favour alcohol minimum unit pricing. Left shift is the notion that in populations the body wags the tail: the mean determines the extremes. Applied to alcohol minimum pricing, left shift has it that if average consumption falls because of raised minimum unit prices, then so too will heavy consumption fall. Populations, according to this hypothesis, behave like a blancmange made with excess gelatine: a nudge in the middle, and the whole pud moves across.

One can be confident that in the drawing room at Downton, Lord G would have something Imperial to say about shifty left footers. Meanwhile, back in the real world, blancmanges of course are rather less well behaved. Putting aside the thorny question of what happens to teetotallers when they get left shifted – presumably they move to negative consumption, and start excreting alcohol – there is no guarantee that the other tail – the heavy drinkers - will feel any great attachment to the body. As anyone who has tried to smooch a blancmange sideways knows, blancmanges have a mind of their own. So too do heavy drinkers.

Left shift may have gained traction amongst Islingtonistas, but we must recall that it is just a hypothesis that has yet to gain empirical support. It started life in the 1950s as the Ledermann single distribution theory, which held that drinking behaviour is distributed lognormally: a skewed lop-sided bell-shape, with an extended right tail. As observations go, this descriptive approximation is fair enough, a ‘good enough’ fit to the reported data. Where the left shift hypothesis/theory/model starts to loose the plot is when what is an observational approximation is given magical predictive powers.

It is a matter of simple sums to show that if we reduce the number and consumption of heavy drinkers, then the average (mean) and spread (scatter, variance, standard deviation) will also fall. We have changed the borders of the distribution, and so the summary numbers that describe it are bound to change. But does it follow that if we change the summary numbers - average consumption, by changing behaviour in the middle of the distribution - then consumption at the tails, the extremes, will also change?

We have already contemplated the black hole of alcohol negative equity that teetotallers face, if only to alert ourselves to the possibility that something dodgy may be going on. The Ledermann/Left Shift hypothesis, and later recipes by Rose, who added the chilling ingredients of first sick and then deviant individuals to the mix, is – to recap - the notion that there is an invisible glue that connects all the individuals in the population together. A movement at the centre will be reflected by a similar movements at the tails: reduce average consumption, and consumption at the tails will also reduce.

For this to work, two connected conditions must be met. Firstly, the population must be homogeneous, that is, one population of like individuals, who all behave in similar ways. The second, which is in its way a statistical expression of the first, is that the spread (scatter, variance, SD) must remain fixed. Indeed, this binding is the glue that connects the tail to the body. Without the glue, the curve (distribution) can become elastic: the body can left shift, while the upper tail remains pinned where it is. Where this leaves the inelastic teetotallers, already facing a negative consumption black hole, doesn’t bear thinking about.

Unless, that is, the fundamental condition for left shift to work – homogeneity, specifically for alcohol-price elasticity - doesn’t apply. As it happens, there is clear evidence it doesn’t. Putting aside for now questions of substitution (switching to a cheaper source to maintain supply, which – by the bye - further weakens the case for minimum pricing), ‘global’ alcohol price elasticity varies greatly by consumption group. Determined teetotallers are, in effect, perfectly price inelastic: no change, however large, in alcohol price will persuade them to touch a drop; and thus they save themselves from negative consumption. Overall, global mean elasticity is around –0.5 (a ten percent increase in price will cause a five percent drop in consumption), while for heavy drinkers, the elasticity is less, at around –0.28. It has even been suggested – not entirely implausibly – that the heaviest drinkers go full circle and join teetotallers with an elasticity of zero - perfect inelasticity: no increase in price, however large, will stop them drinking. The rock on which minimum pricing is built is bust. Minimum unit pricing will never work: it will never achieve its declared aim of delivering left shift, for the simple reason that, in this particular beast, the body and tail are not connected.

To be fair to Rose (the later English proponent of the single distribution theory – Ledermann was French), he worded his classic papers carefully. In Sick Individuals, there is mention of ‘large potential’ – albeit wrapped in hot talk of ‘powerful advantages’, while in Deviants he says: ‘The close link between mean and prevalence [of deviants] implies that to help the minority the “normal” majority must change’ and ‘The way that most people eat, drink, and behave, even if it were harmless to themselves (which is often not the case), may determine how many others, more vulnerable, will suffer as a consequence [italics throughout added]. Rose was careful to sound pious, and yet describe possibilities, not certainties. The pity is that today’s medical Islingtonistas, high on opinion and lite on evidence, have embraced fanciful certainty, and ignored practical reality. That is why, even when he is not playing ShorterTitles, Dr No calls Left Shift left shit.

4 comments:

The move from Classical Liberalism to Neoliberalism is likely the root cause of this confidence, in their own stupidity, displayed by the Islingtonista, a description which seems to encompass most political parties of today. Minimum pricing is much the same as most of the 'healthy living'paradigms that are based in dogma, hearsay and advocacy spawned by 'big food', 'big pharma'and 'big oil' to name but a few.

When Blackdog was just a pup, we ate lard, dripping, eggs, and red meat in abundance and most Doc's had never seen a heart attack victim. Today if we espouse such a lifestyle choice we are viewed as mad or bad. So the professional cowards that rule over us keep banging the same drum without an iota of proof about their naysayings, despite the fact the drivel they speak having had absolutely no effect on society's ill's, in fact probably since about 1965 all health has deteriorated with an acceleration of chronic ailments like Diabetes since about 1984. Strangely this almost exactly coincides with 'fat phobia' and the huge increase in foods specifically marketed to please the Medic's who invented Cholesterol and of course it's lowering.

So the right shit not the left shit is more likely to be responsible DrN', than any leftward movement.

I do have to declare my interest here; I am a lifelong and unreconstructed leftward shiter virtually red through and through, like seaside rock without a centre.

I think you're making the assumption that minimum alchohol measures are aimed at heavy drinkers, Dr No. If that was the case I would agree with you on this. But it's not. In actual fact it is aimed at those in the middle, who may not be alcoholic, but nonetheless are going to incur health problems associated with taking drink that has got progressively stronger over the last decade. Women especially are coming into that category, probably because the average strength of a wine has gone from about 10% to 13% and it isn't helping obesity and diabetes either. The minimum price is a subtler instrument than you think; a supplier can also lower his costs, simply by lowering the percentage in the drink and I actually spoke to one brewery owner who described it as a tax incentive. It is working; you can now buy wines round the 10% mark that aren't simply Weightwatcher's stuff. You are always going to get heavy drinkers and you are always going to get teetotallers, but we have a duty to the people in the middle and that's where this is making the difference.

I keep on running into relatively functional alcoholics on our GI ward, who probably will benefit from these measures. The dysfunctional who will and often have sacrificed everything for alcohol, probably will not. They will spend an ever greater disproportionate amount of there cash on alcohol, to the detriment of their health.

In my opinion you are not right. I am assured. Let's discuss. Write to me in PM, we will communicate.


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