Calculations of the return on investing in a degree are examples of fantasy economics worthy of the greatest scepticism ("Money back guaranteed?", É«ºÐÖ±²¥S , November 8).

The calculation has to be derived from three figures, the first being the lifetime earnings of today's graduates. We shall know those figures in 40 or 50 years' time when those graduates are retiring in a very different economic environment from today's. There is no way of inferring the figure from the earnings of graduates who are retiring today.

The second figure is what that person would have earned in a lifetime if he or she had not gained a degree. We shall not know that figure with any certainty even in 50 years' time: it is certainly not the average lifetime earnings of all those people who did not get degrees.

Third, we need to know what counts as investment in a degree. Presumably this includes fees, but it ought to include living expenses and allow for earnings. These should be compared with what the individual's expenses and earnings might have been had he or she not been taking a full-time degree course.

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Different assumptions have a major effect on the outcome of the calculation - and the results for a part-time course would be found to be different again.

Furthermore, the notion of a return on investment implies that this is a constant ratio, so that doubling the investment would double the return.

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However, a student who doubles his or her investment in higher education by spending the three years of a course on exceptionally riotous living would not be guaranteed a corresponding increase in lifetime earnings.

Anthony Matthew
Computer Centre
Leicester University