In 1906-07, Ladislaus von Bortkiewicz claimed to prove that Marx's account of "the transformation of commodity values into prices of production" (i.e., prices that allow businesses to obtain an average rate of return on their capital investments) was internally inconsistent. "Correcting" the inconsistency, Bortkiewicz produced results that seriously call into question Marx's theory that prices and profits are determined, in the aggregate, by the production of value and surplus-value: the "price rate of profit" no longer equals the "value rate of profit", and the sum of prices diverges from the sum of values. However, proponents of the TSSI claim to have disproved Bortkiewicz's position. Although no critic has successfully refuted this claim, first put forward in 1988, many Marxist economists still decline to accept it.