It is claimed that students who study separate science GCSE are more likely to perform better at A-level science than those who study dual award. This is probably true. It is, however, a mistake to assume that this increase in performance is brought about by the study of the separate science course.

The cohort of separate scientists are self-selected on the basis that they are already good at science before starting GCSE and, therefore, it is no surprise that they perform better at the end of their A-level courses. Your report just informs me that good scientists do well at A-level science.

In fact, the correlation of high performance in A-level history and English seems to suggest that generally more able pupils take separate sciences. This fact is well known.

The only way of drawing a reliable conclusion is to analyse the results of A-level science students who had studied separate sciences and then see what results they would have obtained had they studied dual award. Clearly impossible.

I’m afraid that all such attempts to analyse differing cohorts of students are faced with this problem and it generally leads to bogus claims.

Tony Wilson, Head of science, Birkdale School, Oakholme Road, Sheffield.