A-level students in at least five subjects - biology, English, French, geography and history - achieved about a grade higher in 1998 than candidates of the same general ability did 10 years ago. But maths results have "improved" even more dramatically. Students who gained a C grade in 1988 could have been awarded an A in 1998.
The same trend can be discerned at GCSE, says the author, Dr Robert Coe, of Durham University. The 1994 GCSE candidates would have bettered their results by nearly half a grade, on average, had they taken the exams last year.
His findings will add to the controversy generated by James Sabben-Clare, headmaster of Winchester, who this week told the heads of independent schools that A-levels were easier to pass than they were 20 years ago and were failing to stretch the brightest pupils.
Dr Coe's research compared students' A-level and GCSE scores with their performance in general ability tests. The A-level students in his analysis had taken a 45-minute test of English comprehension and maths - the International Test of Developed Abilities - at the beginning of their course. The GCSE pupils had sat a 25-minute maths and vocabulary test at the start of their fourth year.
All the students attend schools that use Durham University's ALIS (A-level Information System) and YELLIS (Year 11 Information System) to calculate the progress made in the run-up to GCSEs and A-levels. Just over 30,000 A-level students have sat the ITDA test and more than 148,000 have taken the YELLIS test.
While the findings will be seized on by critics of public exams who have consistently complained about "grade inflation", in some respects Dr Coe's study is as inconclusive as the 1996 inquiry into exam standards by the School Curriculum and Assessment Authority. That study tried to establish whether "standards in English, maths and chemistry in exams at 16-plus and 18-plus have been maintained over time". But it was hampered by the number of syllabus changes and the shortage of archived exam scripts.
Dr Coe acknowledges that syllabus changes make it hard to reach definitive conclusions. He also points out that higher grades may have been awarded partly because the quality of teaching has improved and candidates are better prepared for exams.
"Tactics such as paying closer attention to syllabus content, endlessly practising previous years' papers, or being more selective about who is actually allowed to sit the exams, would all help to explain the differences," he says.
The introduction of assessed coursework and modular exams may also have affected results, he believes.
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"Changes in examination grades over time: is the same worth less?", is at www.leeds.ac.ukeducol