People who go to business school with no prior work experience enjoy, on average, a 20% return on their degree. The figure is much lower among people who’ve already held jobs, sinking to just 2.2% for those who’ve worked for 19 years.

These findings emerged from a study of thousands of students by Andrew Hussey, of the University of Memphis, who says that to potential employers, an MBA is primarily a “signalling” device and therefore adds more value when a candidate has a skimpy CV.

Hussey estimates that on average, 90%of the return on an MBA comes from this signalling effect, not from knowledge gained.