Unit Root in the Wage‐Price Spiral Is Not Hysteresis in Unemployment

Hysteresis is one of the main concepts used in Layard, Nickell and Jackman′s book, Unemployment: Macroeconomic Performance and the Labour Market . Attempts to clarify the concept of hysteresis, from its formal representation to its empirical applications. Emphasizes the idea that hysteresis refers back to a given set of formal properties, independently of the phenomenologies within which it is liable to be encountered. In economics, the fields concerned may indeed vary a lot (labour market, foreign trade, etc.). By highlighting all the formal properties of hysteresis, shows how the assimilation of phenomena characterized by a zero eigenvalue for linear systems (or unit‐root systems for discrete‐time processes) is wrong and, moreover, how the imprecise use of the concepts can lead to the particular constraints affecting unit‐root econometrics being overlooked.