Inspired by Piero Sraffa, a new strand of trade theory emerged and was named neo-Ricardian trade theory. The main contributors include Ian Steedman and Stanley Metcalfe. They have criticised neoclassical international trade theory, namely the Heckscher–Ohlin model on the basis that the notion of capital as primary factor has no method of measuring it before the determination of profit rate (thus trapped in a logical vicious circle). This was a second round of the Cambridge capital controversy, this time in the field of international trade. Depoortère and Ravix judge that neo-Ricardian contribution failed without giving effective impact on neoclassical trade theory, because it could not offer "a genuine alternative approach from a classical point of view."