24.1 Macroeconomic Perspectives on Demand and Supply

Macroeconomic Perspectives on Demand and Supply

Aggregate demand and supply are the big-picture versions of regular supply and demand. Instead of looking at one market, they describe how the entire economy behaves. These models help explain how government policies, consumer confidence, and economic shocks affect total output (real GDP) and the overall price level.

One of the most important distinctions in this unit is between the short run and the long run. In the short run, wages and prices are "sticky," so changes in demand affect both output and prices. In the long run, wages and prices fully adjust, so only the price level changes while output returns to its potential level.

Aggregate Demand and Aggregate Supply

Aggregate demand (AD) is the total quantity of goods and services demanded across the economy at each price level. It's made up of four components:

• Consumption spending (C) — household spending on goods and services
• Investment spending (I) — business spending on capital goods, plus residential investment
• Government spending (G) — federal, state, and local government purchases
• Net exports (NX) — exports minus imports

The AD curve slopes downward: as the price level falls, the quantity of goods and services demanded rises. A change in any of these four components shifts the entire AD curve. A rightward shift means higher AD (leading to higher output and a higher price level), while a leftward shift means lower AD (leading to lower output and a lower price level).

Aggregate supply (AS) is the total quantity of goods and services that producers are willing to supply at each price level. There are two versions:

• Short-run aggregate supply (SRAS) slopes upward. Because wages and input prices are slow to adjust, firms produce more when the price level rises (since their revenues increase while costs stay temporarily fixed).
• Long-run aggregate supply (LRAS) is a vertical line at the economy's potential output (also called full-employment output). In the long run, wages and prices fully adjust, so the price level has no effect on how much the economy produces. Output is determined by resources and technology, not by the price level.

Equilibrium occurs where the AD curve intersects the AS curve. That intersection determines both the equilibrium price level and equilibrium real GDP. When AD or AS shifts, the economy moves to a new equilibrium.

Economic growth means the economy's productive capacity increases over time. The main drivers are:

• Technological progress (new inventions, better production methods)
• Human capital accumulation (education, training, skill development)
• Physical capital accumulation (investment in machinery, infrastructure)

On the AD-AS model, economic growth shows up as a rightward shift of the LRAS curve, meaning potential output has increased.

Short-Run and Long-Run Effects

In the short run, sticky wages and prices mean the SRAS curve slopes upward. When AD shifts, both output and the price level change:

• An increase in AD moves the economy up along the SRAS curve, raising both output and the price level.
• A decrease in AD moves the economy down along the SRAS curve, lowering both output and the price level.

In the long run, wages and prices are flexible, so the LRAS curve is vertical at potential output. This has two key implications:

1. Changes in AD only affect the price level in the long run. If AD increases, prices rise but output returns to potential. If AD decreases, prices fall but output still returns to potential. The economy self-corrects as wages and prices adjust.
2. Changes in AS affect long-run output. Factors like technological progress or human capital growth shift the LRAS curve to the right, increasing potential output. Negative supply-side events (destruction of capital, loss of resources) shift LRAS to the left, reducing potential output.

The takeaway: demand-side changes drive short-run fluctuations in output, but long-run output depends on supply-side factors.

Stabilization Policies

Governments and central banks use stabilization policies to smooth out short-run economic fluctuations.

Fiscal policy refers to government decisions about spending and taxation.

• Expansionary fiscal policy: increasing government spending (G) or cutting taxes. This shifts AD to the right, raising output and the price level in the short run.
• Contractionary fiscal policy: decreasing government spending or raising taxes. This shifts AD to the left, lowering output and the price level in the short run.

Monetary policy refers to the central bank's actions to influence the money supply and interest rates.

• Expansionary monetary policy: increasing the money supply or lowering interest rates. This shifts AD to the right, boosting output and raising the price level in the short run.
• Contractionary monetary policy: decreasing the money supply or raising interest rates. This shifts AD to the left, reducing output and lowering the price level in the short run.

Policy limitations are important to understand for exams:

• Time lags: Both fiscal and monetary policy take time to implement and time to affect the economy, which can make stabilization difficult.
• Crowding-out effect: Expansionary fiscal policy often requires government borrowing, which can push interest rates up and reduce private investment, partially offsetting the stimulus.
• Inflationary pressure: Expansionary policies that push output above potential can lead to rising prices.
• Long-run neutrality of money: In the long run, changes in the money supply affect only the price level, not real output. This means monetary policy can't permanently increase GDP beyond potential output.