Despite the central place of the concept of unemployment in macroeconomics, economists devote relatively little attention to the problems attendant on its measurement. Most theoretical discussions assume that a well-defined measure of unemployment is available and econometric studies often use official published unemployment series without discussing their validity. However, specialists in labour economics are aware of the important complications that arise in the measurement of unemployment and of the fact that no single series provides an ideal measure of labour market slack. The issues that arise in this context have been reviewed in several specialised studies (Garvey, 1998; and Royal Statistical Society, 1995).