The concept of the "multiplier" is at the very heart of Keynesian (and therefore macro in general) macroeconomics. The central notion is that when there is an expenditure the money travels from one party to a second party to a third party to a fourth party and on and on and on.
In short, the money is respent and hence multiplied.
The bridge constructed in Cedarville during the summer of 2000 added to the local economy. The initial expenditure by the state added "X" dollars to the economy as the materials, labor, etc. were paid for. In addition the workers ate meals in the area, purchased gas, some may have traveled from outside the region to come to the area to work and stayed in local motels. The initial expenditure by the state added more money to the economy than the simple cost of the bridge. The initial expenditure was multiplied.
multiplier effect -- national income increases by more that the increase in autonomous expenditure
induced and autonomous expenditure
Expenditure may categorized into two categories:
autonomous expenditure -- sum of the components of AE that are not influenced by national income
induced expenditure -- sum of the components of AE that do vary as national income income varies
The basic aggregate expenditure equation:
Further, the initial change will be multiplied. The final change in national income will be larger than the initial change in expenditure.
The following graph illustrates an increase in investment spending as the result of a presidential election. Business people believe the new administration will view business endeavors more favorably than the previous administration.