What are “quack policies”? The name has been coined by the writer Jamie Whyte for policies that are claimed to be based on evidence but which do not stand up to scrutiny. Examples are given in a publication of that name issued by the Institute of Economic Affairs. Leading examples he gives are the attempt to impose a minimum price of alcohol, the attack on “passive smoking”, the global warming crusade and “happiness engineering”. The fact the book is published by the free-market IEA and that the policies he scrutinises find support in the left and centre of the political spectrum (including UK Prime Minister David Cameron) may cause many to ignore it. The loss will be theirs.

There is so much quack policy around that one does not know where to start. Such policies usually start with a genuine concern and exaggerate it in a one-sided way, but above all assume that citizens cannot be trusted to run their affairs. Many such policies are described as evidence-based even though the evidence does not always point to the supposed conclusions. There are two characteristic fallacies. One is that they overlook the benefits that people derive from the discouraged activities. The other is that they ignore the substitutes that are found and can be as harmful as the original. For instance, in Scandinavian countries, which have high alcohol taxes, many more people make their own alcoholic drinks than in other countries.

A more elementary mistake is inadequate reference. How often do we see statements that activity x doubles your chances of getting y. But unless you know what the chances were in the first place the information is of very little value. “Passive smoking” is alleged to increase the incidence of lung cancer among non-smokers. But as incidence of lung cancer among non-smokers is rare – 0.3 per cent – it would require a huge increase to justify banning passive smoking, even if that could be done.