Why the short run aggregate supply curve might shift

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Aggregate supply, also known as total output, is the total supply of goods and services produced within an economy at a given overall price in a given period. It is represented by the aggregate supply curve, which describes the relationship between price levels and the quantity of output that firms are willing to provide. Typically, there is a positive relationship between aggregate supply and the price level.

Aggregate supply is usually calculated over a year because changes in supply tend to lag changes in demand.

Rising prices are typically an indicator that businesses should expand production to meet a higher level of aggregate demand. When demand increases amid constant supply, consumers compete for the goods available and, therefore, pay higher prices. This dynamic induces firms to increase output to sell more goods. The resulting supply increase causes prices to normalize and output to remain elevated.

• Total goods produced at a specific price point for a particular period are aggregate supply.
• Short-term changes in aggregate supply are impacted most significantly by increases or decreases in demand.
• Long-term changes in aggregate supply are impacted most significantly by new technology or other changes in an industry.

A shift in aggregate supply can be attributed to many variables, including changes in the size and quality of labor, technological innovations, an increase in wages, an increase in production costs, changes in producer taxes, and subsidies and changes in inflation. Some of these factors lead to positive changes in aggregate supply while others cause aggregate supply to decline. For example, increased labor efficiency, perhaps through outsourcing or automation, raises supply output by decreasing the labor cost per unit of supply. By contrast, wage increases place downward pressure on aggregate supply by increasing production costs.

In the short run, aggregate supply responds to higher demand (and prices) by increasing the use of current inputs in the production process. In the short run, the level of capital is fixed, and a company cannot, for example, erect a new factory or introduce a new technology to increase production efficiency. Instead, the company ramps up supply by getting more out of its existing factors of production, such as assigning workers more hours or increasing the use of existing technology.

In the long run, however, aggregate supply is not affected by the price level and is driven only by improvements in productivity and efficiency. Such improvements include increases in the level of skill and education among workers, technological advancements, and increases in capital. Certain economic viewpoints, such as the Keynesian theory, assert that long-run aggregate supply is still price elastic up to a certain point. Once this point is reached, supply becomes insensitive to changes in price.

XYZ Corporation produces 100,000 widgets per quarter at a total expense of $1 million, but the cost of a critical component that accounts for 10% of that expense doubles in price because of a shortage of materials or other external factors. In that event, XYZ Corporation could produce only 90,909 widgets if it is still spending $1 million on production. This reduction would represent a decrease in aggregate supply. In this example, the lower aggregate supply could lead to demand exceeding output. That, coupled with the increase in production costs, is likely to lead to a rise in price.

Learning Objectives

• Explain how productivity growth and changes in input prices change the aggregate supply curve

In this section we introduce supply shocks. Supply shocks are events that shift the aggregate supply curve. We defined the AS curve as showing the quantity of real GDP producers will supply at any aggregate price level. When the aggregate supply curve shifts to the right, then at every price level, a greater quantity of real GDP is produced. This is called a positive supply shock. When the AS curve shifts to the left, then at every price level, a lower quantity of real GDP is produced. This is a negative supply shock. This module discusses two of the most important supply shocks: productivity growth and changes in input prices.

How Productivity Growth Shifts the AS Curve

In the long run, the most important factor shifting the AS curve is productivity growth. Productivity means how much output can be produced with a given quantity of inputs. One measure of this is output per worker or GDP per capita. Over time, productivity grows so that the same quantity of labor can produce more output. Historically, the real growth in GDP per capita in an advanced economy like the United States has averaged about 2% to 3% per year, but productivity growth has been faster during certain extended periods like the 1960s and the late 1990s through the early 2000s, or slower during periods like the 1970s. A higher level of productivity shifts the AS curve to the right, because with improved productivity, firms can produce a greater quantity of output at every price level. The interactive graph below (Figure 1) shows an outward shift in productivity over two time periods. The AS curve shifts out from SRAS0 to SRAS1 and LRAS0 to LRAS1, reflecting the rise in potential GDP in this economy, and the equilibrium shifts from E0 to E1.

Figure 1 (Interactive Graph). Shifts in Aggregate Supply. Productivity growth shifts AS to the right.

A shift in the SRAS curve to the right will result in a greater real GDP and downward pressure on the price level, if aggregate demand remains unchanged. However, productivity grows slowly, at best only a few percentage points per year. As a consequence, the resulting shift in SRAS, increase in Q and decrease in P will be relatively small over a few months or even a couple of years.

How Changes in Input Prices Shift the AS Curve

Higher prices for inputs that are widely used across the entire economy, such as labor or energy, can have a macroeconomic impact on aggregate supply. Increases in the price of such inputs represent a negative supply shock, shifting the SRAS curve to shift to the left. This means that at each given price level for outputs, a higher price for inputs will discourage production because it will reduce the possibilities for earning profits. The interactive graph below (Figure 2) shows the aggregate supply curve shifting to the left, from SRAS0 to SRAS1, causing the equilibrium to move from E0 to E1. The movement from the original equilibrium of E0 to the new equilibrium of E1 will bring a nasty set of effects: reduced GDP or recession, higher unemployment because the economy is now further away from potential GDP, and an inflationary higher price level as well. For example, the U.S. economy experienced recessions in 1974–1975, and 1980–1981 that were each preceded or accompanied by a rise in oil prices. In the 1970s, this pattern of a shift to the left in AS leading to a stagnant economy with high unemployment and inflation was nicknamed stagflation.

Figure 2 (Interactive Graph). Shifts in Aggregate Supply. Higher prices for key inputs shifts AS to the left.

Conversely, a decline in the price of a key input like oil, represents a positive supply shock shifting the SRAS curve to the right, providing an incentive for more to be produced at every given price level for outputs. From 1985 to 1986, for example, the average price of crude oil fell by almost half, from $24 a barrel to $12 a barrel. Similarly, from 1997 to 1998, the price of a barrel of crude oil dropped from $17 per barrel to $11 per barrel. In both cases, the plummeting price of oil led to a situation like that presented earlier in Figure 1, where the outward shift of SRAS to the right allowed the economy to expand, unemployment to fall, and inflation to decline.

Along with wages and energy prices, another source of supply shocks is the cost of imported goods that are used as inputs for domestically-produced products. In these cases as well, the lesson is that lower prices for inputs cause SRAS to shift to the right, while higher prices cause it to shift back to the left.

Similarly, an unexpected early freeze could destroy a large number of agricultural crops, a shock that would shift the AS curve to the left since there would be fewer agricultural products available at any given price.

When Does A Supply Shock Shift Potential GDP?

This important question really answers itself. Suppose there is a decrease in aggregate demand, which is shown by a leftward shift in AD, as shown in Figure 2. In the short term, wages are sticky and output decreases along the SRAS, as we move from E1 to E2. Over time, wages decrease and as they do, the SRAS shifts to the right due to the decrease in firms’ cost of production. The SRAS continues to shift until GDP has returned to potential. Graphically, we move from E2 to E3.  Because this event was caused by a demand shock (i.e. a shift in AD), it had no effect on potential GDP. The supply of labor didn’t change, nor did labor productivity so LRAS stays constant, though SRAS shifted. LRAS shifts only when the potential GDP increases or decreases.

Figure 3. A Demand Shock. When AS shifts in response to a shift in AD, potential GDP (and LRAS) is unchanged. Rather, the model adjusts back to the original potential GDP, moving from E1 to E3.

Review things that shift aggregate supply in the following video.

You can view the transcript for “Short-Run Aggregate Supply- Macro Topic 3.3” here (opens in new window).

The video went over the following scenarios. Take a second look and quiz yourself on what will happen to aggregate supply in each situation.

1. A significant increase in nominal wages.
2. An increase in physical capital.
3. A decrease in corporate taxes on producers.
4. An increase in expected inflation.

These questions allow you to get as much practice as you need, as you can click the link at the top of the first question (“Try another version of these questions”) to get a new set of questions. Practice until you feel comfortable doing the questions.

negative supply shock: a leftward shift in the SRAS and LRAS curves positive supply shock: a rightward shift in the SRAS and LRAS curves stagflation: an economy experiences stagnant growth and high inflation at the same time supply shock: an event that shifts both short run and long run aggregate supply curves

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