Dr. Kooyman has made a careful study of the econometric model used around 1963 by the Netherlands Central Planning Bureau, especially of eight of its most import- ant behavioural equations. The Bureau used coefficients estimated from a pre-war and a post-war time series simultaneously, in order to have a larger number of observations. The author, being aware of the difference in general economic 'climate' in the two periods, tests the assumption of no difference in pre-war and post-war coefficients. In an inventive way he uses a few alternat- ive approaches. On the basis of his findings he...