Whitehall figures that just don't add up...

Behind the numbers: In the first of a fortnightly series on the misuse of statistics, we reveal how Labour twisted the data on knife crime

Governments love citing statistics that appear to lend credibility to an otherwise bald and unconvincing narrative. Generally, they get away with it.

People are too mesmerised by the figures to challenge them until it is too late. Time passes, the news moves on, and all that is left is a faint whiff of dishonesty hanging in the air.

But occasionally, to the joy of the populace, politicians and civil servants are caught with their hands actually in the cookie jar. So it was a year ago when the UK Statistics Authority caught the Home Office illicitly citing NHS data to support its claims to have reduced the use of knives in assaults.

The latest data on hospital admissions for assault, published this week, show how misleading these claims were.

In June 2008 the Home Office had launched its Tackling Knives Action Programme (Tkap) in 10 areas of the country, aimed at reducing the carrying and use of knives by teenagers. In December, using NHS data, it claimed that hospital admissions for assault were down by 27 per cent in the July-September quarter compared with the same quarter in 2007.

This was done despite warnings from the NHS Information Centre (IC) that the figures were potentially inaccurate. The Home Office and No 10 simply rolled over the objections from the statistical profession, leading to a stern rebuke from the UK Statistics Authority.

New data released by the IC on Tuesday show, in fact, that the effect of Tkap on admissions for assault is barely perceptible. In the year from October 2007 to September 2008, there were 42,362 admissions for assault in England, 26,475 (62.5 per cent) of them in Tkap areas. In the period from October 2008 to September 2009 there were 43,478 admissions, 27,076 (62.3 per cent) in Tkap areas.

So admissions for assault increased by 2.6 per cent over the year: by 2.3 per cent in Tkap areas and by 3.2 per cent elsewhere. Squinting hard, one might see that as a tiny gain – admissions have risen a fraction more slowly in the Tkap areas than elsewhere. But the difference is so small as to be meaningless.

The Home Office still regards the programme as a success, citing increases in police stop and search activities, and a 13 per cent reduction in teenagers caught in possession of knives (matched by an 8 per cent increase in those over 20 doing so). But it admits that there was no reduction in teenage knife killings in Tkap areas, and a slight increase in killings among those over 20.

Small wonder that against this background, there is a lack of trust in crime statistics. How to restore it is the subject of a meeting on Monday organised by the Statistics Authority. One suggestion it has made is that responsibility for publishing crime statistics should be taken away from the Home Office and given to an independent body, to create some distance between statistics and policy-making.

Nigel Hawkes is Director of Straight Statistics, a campaign for honesty in statistics, www.straightstatistics.org