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.