Flicking through the official figures on the August riots, you could argue that social scientists are once again telling us what we already knew.
To which there are two responses: yes they are, but we needed the evidence; and no, not quite, because the figures are even more disturbing than we'd realised. For they paint a picture of an alienated and potentially criminal faction, detached from mainstream society.
Consider the most basic statistic, earlier revealed by justice secretary Kenneth Clarke, that 76 per cent of defendants linked to the riots - 80 per cent of the adults and 62 per cent of juveniles - had a previous caution or conviction. They had committed an astonishing total of nearly 20,000 previous offences, an average of 11 apiece. The men among them, who comprised 90 per cent of defendants, were each two-and-a-half times more likely on average to have a conviction than a man from the general population.
These statistics come with a drearily consistent life history: of the juvenile defendants, 66 per cent had a special educational need, compared with 21 per cent of all pupils in maintained secondary schools, while 36 per cent had been excluded from school at least once during the previous year, compared with six per cent of all year 11 pupils. At age 11, the defendants' English and maths test results had been around two-thirds of the national average. Put crudely, the rioters were the dropouts whom the education system had failed. Or, you could say, the other way round.
There is one other feature on which right-wing media seized: 46 per cent of defendants were from a black or black mixed race background, 42 per cent were white and only seven per cent were from an Asian or Asian mixed race background. In Haringey, a London borough that includes riot-torn Tottenham as well as leafy Highgate and Muswell Hill, 55 per cent of defendants were black or mixed black, as against 17 per cent of all people under the age of 40. But this was not a universal pattern: in Salford, 94 per cent of defendants were white, almost the same proportion as in the city's general population.
The ethnic classification of the defendants may differ. However, what is undeniable is that these figures signify the emergence of an urban underclass without qualifications, without prospects and socially excluded from all the rest of us: a profoundly disturbing phenomenon.
Sir Peter Hall is Bartlett professor of planning and regeneration, University College London.