RESEARCH into the earnings of identical female twins suggests that an extra year of schooling increases women's earnings by almost 8 per cent on average.
Better-educated people have, of course, always earned more (although teachers may find that hard to believe).
But it is notoriously difficult to work out how much of the extra income can be attributed to education alone because family background, personality and other factors have a bearing on academic and occupational success.
That is why the twins study carried out by researchers at London University and St Thomas's Hospital, appears to have shed extra light on this issue. Jonathan Haskel, of Queen Mary and Westfield College, explains: "Identical twins have exactly the same genes. So if earnings are all determined by genetic make-up they should be the same.
"The identical twins in our data - we had complete wage and scholing information for 214 identical pairs of twins - - also have the same family background. They are the same age, so there is no favouritism to the older or younger sibling, they were brought up together and often went to the same school. If earnings are due to family background, then again the twins should be the same."
However, the study reveals that the identical twins, who were aged 44 on average, had different incomes, strongly correlated with the number of years they spent in the education system.
Twins with between one and four O-levels earned 12 per cent a year more, on average, than those who had none. A-levels raised incomes by a further 10 per cent and degrees by another 6 per cent.
For details contact Jonathan Haskel, Economics Department, Queen Mary and Westfield College, Mile End Road, London E1 4NS.