Looking at past results (for OCR A level for example) I can see that each year approximately 20% of Maths candidates are awarded an A* but only 6% of History candidates.
So it seems this must be a conscious decision to allocate grades in different proportions by subject.
Knowing this might influence choice of A level - if you are much more likely to get a high grade in one subject.
Does anyone know what the justification for this is?