Professor Green discusses the definition of consistent aggregation and the problem of grouping variables in a single equation; he deals with the aggregation of equations and the probable errors; and summarizes, with reference to the text, the considerations involved in selecting an appropriate form of aggregation. The author's survey presents a well-balanced overview and analysis of aggregation, and makes readily accessible for the first time much material otherwise difficult to obtain. Originally published in 1964. The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.