One of Michael Gove's favourite arguments for his school reforms is that Britain has plummeted down the international education league tables. In June 2011 he told Policy Exchange that the UK had fallen from "4th to 16th place in science; from 7th to 25th place in literacy; and from 8th to 28th in maths" between 2000 and 2009 in the OECD's Programme for International Student Assessment (PISA).

But how reliable are the statistics? In this week's NS, Peter Wilby draws attention to a story that deserves more than attention than it has so far received (no national paper has reported on it). Last month, in response to a letter from David Miliband, Andrew Dilnot, the chair of the UK Statistics Authority, expressed "concern" about the Department for Education's unqualified use of the figures. He noted that the OECD's 2009 report for the UK included the following "important caveat":

Trend comparisons, which are a feature of the PISA 2009 reporting are not reported here because for the United Kingdom it is only possible to compare 2006 and 2009 data. As the PISA 2000 and PISA 2003 samples did not meet the PISA response-rate standards, no trend comparisons are possible for these years.

In other words, Gove should not be comparing results from 2000 with those from 2009. Dilnot wrote: "While I understand that some users of these data would like to make comparisons between the first PISA study in 2000 and the most recent in 2009, the weaknesses relating to the response-rate standard in earlier studies should not be ignored."

He concluded: "These uncertainties and weaknesses are not just a technical footnote; they are themselves an important part of the evidence, and affect interpretation and meaning. League tables and the presentation of international rankings can be statistically problematic, and require clear and careful commentary alongside them."

The statistics chief also noted a review published by the Institute for Education which concluded that "problems with identifying change over time" meant the apparent decline in secondary school pupils' performance should not be treated as a "statistically robust result". The Department for Education is yet to respond.

This isn't the only recent instance of the coalition playing fast and loose with statistics. David Cameron is fond of boasting that "one million" new private sector jobs have been created since the coalition came to power, but, as I've noted before, what he doesn't mention is that 196,000 of these were simply reclassified from the public sector.

After complaining for years about Gordon Brown's manipulation of economic statistics, the coalition came to power promising a new era of transparency. But Gove and Cameron's behaviour suggests it's not prepared to practise what it preached.