Included in the reading for the second meeting is a piece by Ann Hagell on population wide prevention, what some call curve shifting prevention. Ann recommends it as a response to knife crime. She draws on the work of Geoffrey Rose. (His book A Strategy of Preventative Medicine has strongly influenced my own work).

Most efforts at social change is focus on the ‘tail of the distribution’, the red area in the graph, the people who drink too much, who are very anti-social, who don’t keep up at school ....

Rose suggests an alternative. Focus on people like me and you. The average drinker, the reasonably behaved, the ones that get by in school.

By getting the average drinker to drink less, or the reasonably behaved person to behave a little better or the middle ranking student to study a little harder, the distribution curve shifts. The tail of the distribution moves. And we end up with fewer alcoholics, fewer angry men and less school dropouts.

This is old stuff. But good stuff. And seriously underused.

But that isn’t the reason for including it in the reading. What I am interested in is why a change of behaviour at one part of the distribution would result in a change at another.

The answer is contagion. Positive contagion. Rose’s work rests on the idea that each person’s behaviour is influenced by and influences others. The amount of alcohol I drink at a party is influenced by the amount of alcohol the other guests drink. Boys carry knives because other boys they know carry knives.

Mark Earls book Herd takes this idea head on. We think we are unique individuals. But in fact we are sheep, following other sheep.