An argument about the accuracy of statistics has broken out after Birmingham’s ruling Tory-Lib Dem coalition was accused of "massaging" the city council's sickness level figures.

Cabinet human resources member Alan Rudge said he was "delighted" to announce that the final figure for absenteeism during 2007/08 was 9.89 days per member of staff compared with 10.25 days a year ago.

But opposition councillors were quick to point out that the new figure is still above the 9.83 days inherited from Labour when the coalition came to power in 2004, despite a four-year drive to cut the amount of time staff take off when they are ill.

Questions were being asked about an apparent sharp drop in projected absenteeism from 10.3 days at the end of February, as reported by Coun Rudge at a council meeting, to 9.89 days at the end of the financial year in April.

The fall was described as inexplicable by Labour group leader Sir Albert Bore, who said a month-by-month analysis of the council’s own projections showed the year-end figure would have to be above 10 days.

Sir Albert (Lab ladywood) added: "It would appear, unless they can provide an explanation, that these figures have been massaged."

Labour also hit out at Coun Rudge for increasing the target for absenteeism rates since 2004.

When the coalition took office, the council’s official policy was to aim to reduce sickness levels to an average nine days, but this was increased to 9.5 days in 2005/06 and to 9.75 days in 2007/08.

Sir Albert added: "They reduced the targets in order to make it easier, but they cannot even hit the easier targets."

The coalition has been determined to reduce absenteeism below the politically sensitive 10-day level, an ambition which has now been achieved if only by the narrowest of margins.

However, concerns remain at the record of the poorest performing departments, including housing and adult social services, where sickness levels are as high as 16 days per employee.

Birmingham is now the best performing of any metropolitan council with regard to staff absenteeism, which peaked in the city at 19 days per employee in 2001. The figures have been falling since then, following the introduction of tough measures to target employees with poor attendance records.

But council leaders are finding it impossible to break decisively below the 10-day mark.

Coun Rudge (Con Sutton Vesey) said: "I am delighted by the final figure that has been recorded for 2007/08. It shows the approach taken by the city council to tackle the problem of staff absence has been successful.

"The last year has seen the council develop and progress its Pay and Grading Review, which, despite the fair offer we have put forward, has left some employees feeling uncertain – so to post improved figures is highly encouraging.

"However, we will not rest on our laurels. We were slightly short of our target for this year of 9.75 days, so it is crucial that we continue to make progress as the council’s productivity will be increased if less time is taken off by staff."