As far as I am aware, candidates may not be entered both for separate science subjects and the double award science at GCSE at the same sitting, so objective evidence for his observation that "candidates of equal ability have been graded lower" in the former than in the latter would be hard to obtain.
From what I know of my local examination board, I am aware that the double award science and the single subject physics, chemistry and biology papers in 1995 contained common questions; and I understand that the board went to extraordinary lengths in order to agree common mark schemes and to ensure comparability of marking. School curriculum and assessment authority-monitored enforcement of the mandatory GCSE code of practice ensured that the standard of the awards made was consistent across subject entries.
Mr Nash's letter seems to imply that awards are norm-referenced. From many years' experience awarding as a senior examiner I can assure him that this is not the case. Indeed, I understand that in 1995 the percentage of candidates awarded grade C or better in separate science subjects increased in comparison with 1994, since it was judged that, on the quality of their work alone, more of them had achieved the standards required. The evidence still seems to suggest that a candidate's ability will be suitably rewarded, whatever examination is taken. It should, of course, go without saying, that A*A* in double award science is only two-thirds of the workload of three A* grades in the separate science subjects. In that sense, it is easier to get a top award in double award than in the separate subjects, but I do not think this is what Mr Nash meant.
T J TURVEY
Hulme Grammar School, Oldham