Numerical drift

I see from your report (3 December) that Scotland scores a higher mark than England in the PISA assessment on mathematics.

What is more intriguing is that both countries, with marks of 498 and 495, exceed the UK figure of 494.

I hope that Wales and Northern Ireland do not provide the dead weight to drag the average down. I would guess, however, that the old escape clause of “rounding error” will provide the explanation.

If so, it suggests that some statistics are ill fitted to bear the interpretations put on them. Maybe they have caught the current ailment affecting numbers in wider debates.

LV McEwan

Edinburgh