STATISTICAL DEVICES USED IN FORE
The materials with which the student of business conditions must work consist almost entirely of statistical series. Series relating to past business cycles are analyzed in order to discover typical sequences and formulate principles of general applicability, while series relating to the present and the immediate past are the most important data to be used in making practical application of the forecaster's theoretical knowledge. Some information comes in the form of general knowledge concerning the state of trade, the efficiency of labor, the attitude of the speculative public, the political outlook, and other conditions which cannot be reduced to the form of numerical items, but much the most important part of the task of the forecaster consists in the interpretation of series of statistical data.1 It is, therefore, necessary to give some attention to the choice of series and to the questions of method which arise in connection with them.
The most useful data for the student of business conditions are those which appear in monthly form. Annual data are of almost no use in studying the____________________