Dr Sinclair's misuse of statistics to imply that 99.99 per cent of GCSE grades are accurate cannot go unchallenged ("Disputed Marks", Letters, February 15).
The number of grades changed due to enquiries and appeals does indeed represent a small proportion of all GCSE results - about 0.2 per cent in 2006. But this figure tells us nothing about the accuracy of marking in the vast majority of cases where, for whatever reason, the result is not challenged.
A more meaningful statistic is that more than 23 per cent of GCSE re-mark enquiries made between 2003-6 resulted in a grade change. In other words, for every five enquiries, at least one resulted in a higher grade being awarded. At A-level, where stakes are higher, the situation was little better, with approximately 11 per cent of enquiries resulting in a grade change.
Finally, I cannot accept Dr Sinclair's assertion that "requests for re-marks are clustered just short of grade boundaries". We know that the number of raw marks between grade thresholds on individual examination components is generally small, so it would be surprising if schools were targeting their enquiries in the way described - other than, perhaps, below the AB cut-score!
George Bethell, Director, Anglia Assessment.