Rory Sutherland Columnist When individual persuasion leads to social contagion T smokers (or non-quitters) in the group by two. And this ignores any he argument for banning smoking in public places was effects the new smoker may have on people outside the group. largely won on the basis of passive smoking. Once it But, even though it is scientifically far more convincing, we had been shown that smoking was harmful to probably would not have accepted the argument as sufficient to non-smokers, a convincing case could be made for a justify a ban. It strikes at our deep-felt belief in individual agency. The ban in the interests of protecting the innocent bystander. unshakeable notion that we are and should be the exclusive Yet, the scientific evidence was far from watertight. Many studies authors of our own behaviour. Im as guilty of this delusion as had shown no link between exposure to second-hand smoke and ill anyone; I worked with Mark Earls when he was writing Herd, yet it health; indeed, more frustratingly for health campaigners, some even took me some years to realise that he was fundamentally right. suggested that a non-smoker was slightly better off living with a Yet, most large-scale changes in attitude and behaviour have smoker than in a smoke-free household. Although counterintuitive, perhaps succeeded more as the product of social contagion than this finding is not impossible there are quite a few areas of human individual persuasion. The widespread acceptance of same-sex health where mild exposure to toxins is better than none at all. marriage. The decline in drink-driving. The rapid decline in overt Bluntly, the smoking ban was justified on the back of some rather racial prejudice. Not dropping litter. Wearing denim. All have come dodgy statistical science more policy-based evidence-making than about more through the wider social force of imitation than evidence-based policy-making. A few scientists dissented. individual agency. Interviewed on Radio 4 late in life, Sir Richard Doll, who was among Yet, it remains the force that dare not speak its name. Economics the first group of scientists to establish a link between smoking and is based on the idea of methodological lung cancer in 1950, pronounced individualism. This means that, when himself completely unconcerned by the we measure the effect of legislation or presence of smokers. Conventional approaches incentives, we only look for the initial And yet, the smoking ban has proved to measuring advertising may effect on individual behaviour not the to be a huge success. cause us to do it least where it is magnified social effect that comes later. The smoking ban is an example of a needed most This may cause us to hugely right thing done for the wrong reason. underrate the value of marketing and Writing in his latest book Under the to misdirect it. It seems entirely Influence, Professor Robert Frank, a plausible to me that, when I buy an electric car in April, it will cause friend and one of my behavioural heroes, has proposed a much more two other people to buy one (frankly, Im only getting one because robust justification for the smoking ban and a far better explanation my brother has one). Likewise, if I were to install solar panels, my for why it worked so well. The act of smoking encourages other action may be three times more effective at cutting CO2 emissions people in your peer group to smoke. Hence, driving smoking out of mainstream social life removed the copycat instinct that made than I think, because it encourages my neighbours to do the same. starting smoking easier and quitting harder. Yet, in the very early stages, advertising for solar panels might As Frank convincingly points out, the harm that arises when you appear to be very ineffective, precisely because they are rare, and allow people to smoke freely in public arises far more from social seeding an unusual behaviour is hard. But that is precisely when contagion than from chemical exposure. The visible presence of any mass advertising may work best. Later, when solar panels become smoker in a group of friends hugely increased the odds that others in more commonplace, and that sigmoid adoption curve starts the group would take up smoking, or that smokers would fail to quit. bending steeply upwards, my advertising will look extraordinarily Even after correcting for the natural tendency of people who share effective, when much of the heavy lifting is being done by social a vice to cluster together, research cited by Frank shows that, in a imitation instead. group of five people where one smokes, if one additional person If this is so, conventional approaches to measuring advertising may takes up smoking in that group, it will increase the likely number of cause us to do it least where it is needed most. And vice versa. 7