To STUDY THE CAUSES of income distribution and its changes, it is necessary to formulate and test hypothetical random differential equationis describing the individual income growth in probability terms. Assume that everyone has started in 1910 with the same income, and that each subsequent year one-half of the families, chosen each year at random, has an income raise, the other half an income cut, of $1.00 a year. With a constant population, the mean income (a measure of prosperity) would remain the same. But the standard deviation would grow as the square root of time, because the variance of the sum of t independent random variables is equal to the sum of their t variances, which, in our case, are all equal. Hence, if the coefficient of variation (standard deviation divided by the mean) is used as the inequality measure, the inequality would turn out 10 per cent higher in 1933 than in 1929 (because /23: /19 =1.1) although, under the above assumptions there would have been no boom in the latter and no depression in the former year. Other inequality measures yield analogous results. As the second, more general example, denote by rt the income of a given family at time t, and by X a normally distributed variate with zero mean and with standard deviation (the same for all families and independent of time) o. If the individual income changes according to the random differential equation

WE ipropose to outline a method for deriving optimal rules of inventory policy for finished goods. The problem of inventories exists not only for business enterprises but also for nonprofit agencies such as governmental establishments and their various branches. Moreover, the concept of inventories can be generalized so as to include not only goods but also disposable reserves of manpower as well as various stand-by devices. Also, while inventories of finished goods present the simplest problem, the concept can be extended to goods which can be transformed, at a cost, into one or more kinds of finished goods if and when

J. Tinbergen, Tjalling C. Koopmans, Jacob Marschak, Francois Divisia, Jacques Rueff, B. Chait, La loi de divergence: Discussion, Econometrica, Vol. 17, Supplement: Report of the Washington Meeting (Jul., 1949), pp. 124-128