In a debate at its conference in Aviemore yesterday, the Scottish Police Federation passed a resolution calling for a review of Scottish crime statistics, after hearing claims that they had been manipulated in such a way as to conceal from the public the true extent of crime in Scotland.

The motion was moved by a constable from Strathclyde Police, Fiona Morris, who said that the figures had been altered by counting several crimes that had taken place at the same time as a single crime. This practice of “subsuming” several crimes into a single crime had recently been extended, she claimed, to include crimes such as murder, attempted murder, and robbery. The motion was supported by 60 per cent of delegates, The Scotsman reports.

If true, this is a serious charge. There are rules for counting crimes which should prevent any such manipulation. The Scottish Government has said the the claims are completely untrue.

The Scottish National Party has made much of the fall in crime since it took office in May 2007. In its election manifesto for the 2011 election the SNP said that crime rates had fallen by a fifth since it came to power and were now at their lowest level for 32 years. The official statistics for police-recorded crime back the claim, recording a fall from 419,257 in 2006-07 to 338,028 in 2009-10, or 19.4 per cent.

The 2009-10 figures were the most recent then available. But since then the 2010-11 figures have been published, showing a further fall, to 323,060. This represents a 22.9 per cent decline between 2006-07 and 2010-11 – good news.

But has this been achieved by chicanery, as PC Morris alleged? There’s nothing in the statistics to suggest this – no implausible falls in any particular category of crime. Not does there appear to have been an official change in the counting rules. (There was one for breaches of the peace as a result of the Criminal Justice and Licensing Scotland Act of 2010, but these are classified as offences not crimes and are not part of the SNP claim. Offences have fallen by 12.7 per cent since 2006-07, rather more slowly than crimes.)

There are two possible truth checks we might apply to the recorded crime statistics. One is to compare them with recorded crime in England & Wales, and the other is to compare them with the Scottish Crime and Justice Survey, which asks people if they have been victims of crime.

Comparing Scotland with England and Wales for recorded crime, the falls are almost identical – 22.9 per cent for Scotland since 2006-07, and 23.5 per cent for England and Wales over the same period (see Table). True, the definition of crimes and the ways they are counted are not identical, but the fact that recorded crime has fallen at almost exactly the same rate in both jurisdictions gives no reason to doubt the Scottish figures. (Nor does it suggest the Scottish declines were achieved by any special SNP magic that was absent south of the border.)

The survey data does not cover exactly the same period, since before 2008 the SCJS was based on a much smaller sample and had wider confidence intervals, but the figures for 2008-09 and 2010-11 show a statistically significant fall of 16 per cent. The numbers, of course, are different – surveys count far more crimes than are recorded by the police – but the trend is in the same direction and of much the same magnitude.

There is little here to suggest the charges made at the conference have, even if true, had a significant impact on the statistics.