DISCUSSIONS OF IDENTIFICATION of parameters in simultaneous equation econometric models almost invariably assume that data are in the form of aggregative time series, i.e., only one measurement of each variable is available in each time period. This note shows that parameters in a model which is underidentified by the usual rank and order criteria at the aggregative level may be identified when disaggregated data aie available. The argument is presented in terms of a traditional textbook example of an underidentified model which consists of a demand and a supply function for a single commodity that are linear in price, and a market clearing equilibrium equation.

[This paper investigates the justification for the competitive assumption that consumers will act as price takers by considering the utility gain an individual can achieve by manipulating price formation through the use of non-competitive behavior. Although announcing one's competitive demand is generally not a best replay against the excess demand of the rest of the economy, we show that, as the number of consumers becomes large, the gain any one can achieve acting monopolistically goes to zero if the increase in numbers comes through replication or if the sequence of economies converges to an economy at which the equilibrium price correspondence is continuous.]