3.3 Short-Run Aggregate Supply (SRAS)

SRAS Curve AP Macro Summary

Short-run aggregate supply (SRAS) shows the positive relationship between the price level and the real GDP that firms produce. It slopes upward because wages and some prices are sticky in the short run, and it shifts when production costs change. Along the SRAS curve, a higher price level means more output and lower unemployment, which is the short-run trade-off between inflation and unemployment.

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Why This Matters for the AP Macroeconomics Exam

SRAS is one half of the AD-AS model, the core tool in AP Macroeconomics for explaining output, employment, and the price level. You will use it to interpret past outcomes and predict how shocks and policies change the economy in the short run. Expect to draw and read AD-AS graphs, decide whether an event moves you along SRAS or shifts it, and explain cause-and-effect chains in writing. Getting SRAS right also sets up later topics like long-run self-adjustment and the Phillips curve.

Key Takeaways

• SRAS shows the relationship between the price level and the quantity of real GDP firms supply, and it is upward-sloping because wages and prices are sticky in the short run.
• A change in the price level causes a movement along SRAS, not a shift.
• Any factor that changes production costs shifts SRAS: higher costs shift it left, lower costs shift it right.
• A change in inflationary expectations changes production costs and shifts SRAS.
• Moving up along SRAS, higher output means more employment, so unemployment falls. This is the short-run trade-off between inflation and unemployment.
• Always label your axes "Price Level" and "Real GDP," not "Price" and "Quantity."

What SRAS Is

Short-run aggregate supply represents all the goods and services that firms are willing and able to produce at various price levels. The relationship between the price level and real GDP supplied is positive: as the price level rises, firms produce more real GDP, and as the price level falls, firms produce less.

This looks a lot like the law of supply for a single good, but the axes are different. On an AD-AS graph the vertical axis is the Price Level and the horizontal axis is Real GDP.

Why SRAS Slopes Upward

SRAS is upward-sloping because wages and some resource prices are sticky in the short run. Sticky means they do not adjust right away. Many wages are locked in by contracts, and some prices are slow to change. When the price level rises but input costs stay fixed for a while, producing extra output becomes more profitable, so firms increase output. When the price level falls but costs stay fixed, firms cut back.

A change in the price level is a movement along SRAS. It is not a shift. This is one of the most common errors on the exam, so keep it straight.

What Shifts SRAS

A shift happens when something other than the price level changes how much firms produce at every price level. The key driver is a change in production costs:

• If nominal wages or other input costs rise, firms produce less at every price level, so SRAS shifts left.
• If production costs fall, firms produce more at every price level, so SRAS shifts right.

One important cause of changing production costs is a change in inflationary expectations. If workers and firms expect higher inflation, they build higher wages and costs into contracts. That raises production costs and shifts SRAS left.

Many study resources use the acronym RAP to group SRAS shifters as an organizing tool:

• Resource prices and availability
• Actions of the government, such as taxes and regulations
• Productivity and technology

These all work by changing production costs. Anything tied to the price level moves you along SRAS, while these other factors shift the whole curve right or left.

The Short-Run Trade-Off Between Inflation and Unemployment

Moving up along the SRAS curve, a higher price level is associated with greater real output. To produce more output, firms hire more workers, so employment rises. If the labor force is held constant, higher employment means unemployment falls. So in the short run there is a trade-off between inflation and unemployment along the SRAS curve. This idea connects directly to the Phillips curve you will see later in the course.

Practice Scenarios

For each event, decide whether SRAS increases (shifts right), decreases (shifts left), or whether it is just a movement along the curve.

• The Canadian Prime Minister places new regulations on carbon emissions. SRAS decreases (shifts left). A government regulation that raises production costs reduces the quantity supplied at every price level.
• An increase in consumer income causes the GDP deflator to rise to 110. A rising GDP deflator signals a higher price level. On SRAS, a higher price level leads firms to produce more real GDP in the short run. This is a movement up along SRAS, not a shift.
• Automation in the workplace doubles productivity for all firms in Japan. SRAS increases (shifts right). New technology makes firms more productive at every price level, lowering production costs.
• A war harms a country's coal refineries. SRAS decreases (shifts left). This reduces resource availability, so there is less of a key input, and firms produce less at every price level.

How to Use This on the AP Macroeconomics Exam

Multiple Choice

• First ask: did the price level change, or did something else change? Price level change means movement along SRAS. Anything else means a shift.
• For shifters, trace the logic through production costs. Higher costs shift SRAS left; lower costs shift SRAS right.
• Watch for expectations questions. Higher expected inflation raises costs and shifts SRAS left.

Free Response

• Draw a correctly labeled AD-AS graph with "Price Level" on the vertical axis and "Real GDP" on the horizontal axis.
• Show shifts with a new curve and a clear direction (label SRAS1 and SRAS2). Show movements as a new point on the same curve.
• Explain the chain of cause and effect in words, not just the graph. For a leftward SRAS shift, say production costs rose, so output falls and the price level rises.
• When asked about employment, connect output to hiring: more output means more employment and lower unemployment, holding the labor force constant.

Common Trap

• Do not treat a price level change as a shift. That is a movement along the curve.
• Do not label your axes "Price" and "Quantity." That is the single-market supply and demand model, not AD-AS.

Common Misconceptions

• SRAS and single-good supply are the same. They look similar, but SRAS uses Price Level and Real GDP, and it describes the whole economy, not one product.
• A price level change shifts SRAS. A price level change is a movement along SRAS. Only changes in production costs (or other non-price factors) shift it.
• Higher inflationary expectations shift SRAS right. They actually shift SRAS left, because expected higher inflation raises wages and input costs.
• A leftward SRAS shift lowers the price level. A leftward shift raises the price level while lowering output. This is cost-push inflation.
• More output has no link to unemployment. Producing more output requires more workers, so along SRAS, higher output means lower unemployment when the labor force is held constant.

Related AP Macroeconomics Guides

• 3.1 Aggregate Demand
• 3.2 Spending and Tax Multipliers
• 3.4 Long-Run Aggregate Supply (LRAS)
• 3.8 Fiscal Policy
• 3.5 Equilibrium in Aggregate Demand-Aggregate Supply (AD-AS) Model
• 3.6 Changes in the AD-AS Model in the Short Run