Econometrics may be defined as the quantitative analysis of actual economic phenomena based on the concurrent development of theory and observation, … - Tjalling Koopmans

It is worth pointing out that in this particular study our authors have abandoned demand and supply functions as a tool for analysis, even as applied to individuals... [The problem] has been reformulated as one of proving that a number of maximizations of individual goals under interdependent restraints can be simultaneously carried out.

According to a frequently cited definition, economics is the study of “best use of scarce resources.” The definition is incomplete. “Second best” use of resources, and outright wasteful uses, have equal claim to attention. They are the other side of the coin.

The principal customers aimed for are other economists or members of other professions, who are somewhat closer to the making of policy recommendations... The question of the clientèle is even more baffling when the problem concerns growth paths for time spans covering several generations. What can at best be recommended in that case is the signal the present generation gives, the tradition it seeks to strengthen or establish, for succeeding generations to take off from.