Long-Run Aggregate Supply — AP Macroeconomics
1. Definition and Shape of LRAS ★★☆☆☆ ⏱ 4 min
Long-Run Aggregate Supply (LRAS) represents the relationship between the aggregate price level and the total quantity of real GDP supplied by all firms in an economy after all nominal input prices (including wages, raw material contracts, and rental rates) are fully flexible and able to adjust to market shocks. Unlike the short run, where nominal prices are often sticky, the long run allows full adjustment to shocks, so changes in the aggregate price level do not change the overall quantity of output the economy can produce at full employment.
LRAS is a core concept in AP Macroeconomics Unit 3, which accounts for 10–15% of total AP exam weight. It appears regularly on both multiple-choice and free-response sections, and forms the foundation for all long-run analysis of growth, recessions, and inflation.
The standard LRAS curve expected on the AP exam is perfectly vertical at potential output. This shape follows from the core long-run assumption that all nominal prices and wages are fully flexible. If aggregate demand increases, pushing up the aggregate price level, nominal wages will eventually rise proportionally to match the higher price level, restoring real wages to their original level. Firms have no incentive to increase output beyond potential, because their production costs rise proportionally with output prices. If aggregate demand decreases, pushing the price level down, nominal wages eventually fall proportionally, so firms have no incentive to cut output below potential. Early Keynesian theory proposed a horizontal LRAS in deep depressions, but this rare extreme case is not tested on the AP exam.
Exam tip: On AP FRQs, always draw LRAS as a perfectly vertical line; explicitly state it is vertical because full-employment output is independent of the aggregate price level in the long run to earn full points.
2. Shifts of the LRAS Curve ★★★☆☆ ⏱ 4 min
LRAS shifts only when potential output $Y_p$ changes, which occurs when the economy's long-run productive capacity changes. Anything that changes the quantity or quality of factors of production (labor, physical capital, human capital, technology, natural resources) or institutions that support production (property rights, regulatory efficiency) will shift LRAS. Increases in productive capacity shift LRAS right; decreases shift LRAS left.
A key AP exam rule: any permanent change that shifts short-run aggregate supply (SRAS) will also shift LRAS. Only temporary supply shocks (e.g., a one-year drought that raises grain prices, a temporary oil price cut) shift SRAS without shifting LRAS. For example, a permanent improvement in agricultural technology that permanently lowers food production costs shifts both SRAS and LRAS right, while a temporary bumper corn crop only shifts SRAS right.
Exam tip: When asked what shifts LRAS, remember: only permanent changes in productive capacity shift LRAS. Temporary price changes or demand shocks never shift LRAS, even if they shift SRAS.
3. Long-Run Macroeconomic Equilibrium ★★★☆☆ ⏱ 4 min
Long-run macroeconomic equilibrium occurs when aggregate demand (AD), short-run aggregate supply (SRAS), and LRAS all intersect at the same point. At this equilibrium, real GDP equals potential output ($Y = Y_p$) and unemployment equals the natural rate ($u = u_n$).
If the economy is in short-run equilibrium but not long-run equilibrium, an output gap exists: $\text{Output Gap} = Y - Y_p$. A positive output gap ($Y > Y_p$) is an inflationary gap, with unemployment below the natural rate. A negative output gap ($Y < Y_p$) is a recessionary gap, with unemployment above the natural rate. In the classical self-correcting mechanism, the economy automatically adjusts back to long-run equilibrium at LRAS without government intervention: input prices adjust, shifting SRAS until output returns to $Y_p$. LRAS itself does not shift during this adjustment process, because productive capacity has not changed.
Exam tip: Never shift LRAS in the self-correction process after a demand shock; only SRAS shifts to bring output back to the existing LRAS level of potential output.
4. AP-Style Concept Check ★★★★☆ ⏱ 2 min
Common Pitfalls
Why: Students confuse temporary and permanent supply shocks, often shifting LRAS any time SRAS shifts.
Why: Students mix up short-run and long-run assumptions of price/wage stickiness vs flexibility.
Why: Students confuse short-run and long-run effects of demand policy.
Why: Students confuse output gap definitions, incorrectly thinking potential output is higher than full employment output.
Why: Students confuse demand-side fiscal policy with supply-side policies that change productive capacity.
Why: Students mix up the relationship between natural unemployment and potential output.