LABOR FORCE DYNAMICS
THE GROSS MOVEMENT of persons in and out of the labor force during a year ("labor force mobility") can be contrasted with net movements of persons in or out of the labor force. Net changes, as measured by differences in the monthly survey statistics, can in turn be classified as seasonal (those changes that occur in a regular pattern during consecutive twelve-month intervals), cyclical (changes that tend to coincide with the fluctuations of general business activity over a period of more than a year), and long-run (changes occurring over a period of a number of cycles).
In this chapter we shall be concerned with net changes in the labor force. We shall not simply describe what they are or have been, however; rather, we shall attempt to isolate and appraise some of the economic factors that explain them.
In general, the size of the labor force of the United States reaches a seasonal low in the first quarter of the year and rises with the spring expansion of agricultural activities, construction, and other outdoor work. In May and June, as students leave school to enter the labor force, it expands sharply until it reaches a peak in July. In September the seasonal contraction begins as students return to school and as outdoor activities in construction and agriculture begin to taper off, and the labor force then