In 1976, you published an article of mine on comparability of grades, a topic which has arisen again in connection with A-levels. I wrote then: “In 1968, the London O-level chemistry exam consisted of one three-hour paper with question choice, and the description of the syllabus in the regulations covered two pages. In 1976, the same exam (from a certification point of view) consisted of a multiple-choice paper lasting 75 minutes and a two-hour paper comprising, in one section, six compulsory structured questions and, in the other, four essay questions from which candidates had to answer two.

“Meanwhile, the syllabus had grown to 12 pages in the regulations, including a booklist where there was none before. It seems to me quite likely that in 1968, with the dependence on one examining technique only, the exam failed to assess adequately what many candidates had learned, whereas now (in 1976), with the inclusion of more techniques, there is more opportunity for candidates to reveal what they know. Alternatively, one could argue that both exams were appropriate to their syllabuses but that the versions of chemistry learned and examined were not the same. Either way, comparability of grades between the two years means very little.”

ROBERT WOOD

83 London Road Knebworth, Hertfordshire