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A Shift in Aggregate Demand: An Increase in Government Purchases

25 April, 2016 - 09:12

Suppose an economy is initially in equilibrium at potential output YP as in Figure 22.11. Because the economy is operating at its potential, the labor market must be in equilibrium; the quantities of labor demanded and supplied are equal.

Now suppose aggregate demand increases because one or more of its components (consumption, investment, government purchases, and net exports) has increased at each price level. For example, suppose government purchases increase. The aggregate demand curve shifts from AD1 to AD2 in Figure 22.11. That will increase real GDP to Y2 and force the price level up to P2 in the short run. The higher price level, combined with a fixed nominal wage, results in a lower real wage. Firms employ more workers to supply the increased output.

The economy’s new production level Y2 exceeds potential output. Employment exceeds its natural level. The economy with output of Y2 and price level of P2 is only in short-run equilibrium; there is an inflationary gap equal to the difference between Y2 and YP. Because real GDP is above potential, there will be pressure on prices to rise further.

Ultimately, the nominal wage will rise as workers seek to restore their lost purchasing power. As the nominal wage rises, the short-run aggregate supply curve will begin shifting to the left. It will continue to shift as long as the nominal wage rises, and the nominal wage will rise as long as there is an inflationary gap. These shifts in short-run aggregate supply, however, will reduce real GDP and thus begin to close this gap. When the short-run aggregate supply curve reaches SRAS2, the economy will have returned to its potential output, and mployment will have returned to its natural level. These adjustments will close the inflationary gap.

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Figure 22.11 A shift in Short-Run Aggregate Supply: An Increase in the Cost of Health Care

Again suppose, with an aggregate demand curve at AD1 and a short-run aggregate supply at SRAS1, an economy is initially in equilibrium at its potential output YP, at a price level of P1, as shown in Figure 22.12. Now suppose that the short-run aggregate supply curve shifts owing to a rise in the cost of health care. As we explained earlier, because health insurance premiums are paid primarily by firms for their workers, an increase in premiums raises the cost of production and causes a reduction in the short-run aggregate supply curve from SRAS1 to SRAS2.

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Figure 22.12 Long-Run Adjustment to a Recessionary Gap

As a result, the price level rises to P2 and real GDP falls to Y2. The economy now has a recessionary gap equal to the difference between YP and Y2. Notice that this situation is particularly disagreeable, because both unemployment and the price level rose.

With real GDP below potential, though, there will eventually be pressure on the price level to fall. Increased unemployment also puts pressure on nominal wages to fall. In the long run, the short-run aggregate supply curve shifts back to SRAS1. In this case, real GDP returns to potential at YP, the price level falls back to P1, and employment returns to its natural level. These adjustments will close the recessionary gap.

How sticky prices and nominal wages are will determine the time it takes for the economy to return to potential. People often expect the government or the central bank to respond in some way to try to close gaps. This issue is addressed next.