AP Macroeconomics: Phillips Curve

The relationship between inflation and unemployment is one of the most crucial, and debated, concepts in macroeconomics. For policymakers, understanding this trade-off—or lack thereof—is essential for making decisions about interest rates and government spending. The Phillips Curve models this dynamic, but its implications change dramatically depending on whether you are analyzing the short run or the long run.

The Short-Run Phillips Curve: The Apparent Trade-Off

The original short-run Phillips curve depicts an inverse relationship between the rate of inflation and the rate of unemployment. When unemployment is low, inflation tends to be high, and vice versa. This happens because a tight labor market (low unemployment) gives workers more bargaining power, leading to higher wages. Businesses, facing higher labor costs, often raise prices to maintain profits, resulting in inflation. Conversely, high unemployment weakens workers' bargaining power, leading to slower wage growth and lower inflation.

Imagine a simple economy where consumer demand suddenly surges. Businesses ramp up production and hire more workers, reducing unemployment. As they compete for a smaller pool of available workers, they must offer higher wages. These increased costs are then passed on to consumers in the form of higher prices. In this scenario, you can see the short-run trade-off in action: lower unemployment is "purchased" at the cost of higher inflation. Graphically, this is represented by a downward-sloping curve.

Expectations and the Shifting Curve: Adaptive vs. Rational

The short-run Phillips curve is not stable. It can shift due to changes in inflation expectations. This leads us to the expectations-augmented Phillips curve. The core idea is that workers and firms don't just care about nominal wages and prices; they care about real values—what their money can actually buy. If everyone expects 3% inflation next year, workers will demand at least a 3% raise just to maintain their purchasing power, and firms will plan for 3% higher prices.

The model of adaptive expectations assumes people form their expectations of future inflation based on recently observed inflation. If inflation was 5% last year, they expect roughly 5% this year. Under this view, the short-run Phillips curve shifts upward when actual inflation rises, as expectations catch up with reality. A policy aimed at lowering unemployment below its natural rate only works until people adapt their expectations, at which point unemployment returns to its original level but with higher ongoing inflation.

Rational expectations is a more modern hypothesis suggesting that individuals use all available information, including an understanding of government policy, to forecast the future. If the public believes the central bank will engage in expansionary policy, they will immediately adjust their inflation expectations upward. In its strongest form, this theory implies that predictable policy actions cannot systematically lower unemployment even in the short run, as markets adjust almost instantly.

The Long-Run Phillips Curve and the Natural Rate

The adjustment of expectations brings us to the most critical insight: the long-run Phillips curve at natural rate. In the long run, after all expectations have fully adjusted, there is no stable trade-off between inflation and unemployment. The economy returns to its natural rate of unemployment (NRU), which is determined by structural factors like technology, demographics, and labor market institutions (e.g., minimum wage laws, unionization).

The long-run Phillips curve is vertical at the NRU. This means that while different inflation rates are possible in the long run, unemployment will always gravitate back to its natural level. Attempts to use monetary or fiscal policy to peg unemployment permanently below the NRU will only lead to ever-accelerating inflation, as policymakers constantly have to "surprise" the public to achieve the short-run gain. The vertical long-run curve underscores that sustainable reductions in unemployment require structural policies, not just demand management.

Stagflation and the Breakdown of the Simple Model

The phenomenon of stagflation—the simultaneous occurrence of high inflation and high unemployment—shattered the early belief in a stable Phillips curve trade-off. In the 1970s, supply shocks (like the OPEC oil embargo) increased production costs for businesses across the economy. This caused a sharp rise in prices (inflation) while also forcing firms to cut back on production and lay off workers (increasing unemployment).

On a graph, stagflation is represented by a rightward shift of the short-run Phillips curve. The entire trade-off deteriorates: for any given rate of unemployment, the associated inflation rate is now higher. Stagflation demonstrated that the Phillips curve relationship is not just about demand-side factors; negative supply shocks can worsen both problems at once, moving the economy to a less desirable point on the inflation-unemployment spectrum.

Policy Implications of the Inflation-Unemployment Relationship

Understanding the different Phillips curves leads to powerful policy lessons. First, policymakers face a short-run trade-off. In a recession, expansionary policy can reduce unemployment at the cost of some inflation. However, the second lesson is that this trade-off is temporary. The benefits will erode as expectations adjust.

The third, and most important, implication is the primacy of anchoring inflation expectations. If a central bank can convince the public that it is committed to low, stable inflation (e.g., a 2% target), then the short-run Phillips curve will be positioned more favorably. With well-anchored expectations, a negative demand shock might cause less inflation to fall for a given rise in unemployment. This makes the economy easier to stabilize. Finally, these models argue that the best long-run contribution of monetary policy is to control inflation, while structural policies address the natural rate of unemployment.

Common Pitfalls

1. Believing the trade-off is permanent: The most frequent mistake is confusing the short-run and long-run curves. Remember, the downward-sloping trade-off only exists in the short run when inflation expectations are not yet fully adjusted. In the long run, the curve is vertical.
2. Misidentifying shifts along vs. shifts of the curve: A movement along a fixed short-run Phillips curve is caused by changes in aggregate demand (e.g., expansionary policy). A shift of the entire short-run curve is caused by changes in inflation expectations or by supply shocks (like stagflation).
3. Confusing adaptive and rational expectations: Adaptive expectations are backward-looking and adjust slowly; rational expectations are forward-looking and incorporate all information. The policy implications differ significantly. Under adaptive expectations, policy can have short-run real effects. Under strong rational expectations, predictable policy may be ineffective.
4. Forgetting supply shocks: Students often explain all inflation with demand-side factors. Stagflation is the classic counterexample, showing how cost-push (supply-side) shocks can shift the short-run Phillips curve outward, worsening both inflation and unemployment simultaneously.

Summary

• The short-run Phillips curve shows a temporary inverse trade-off between inflation and unemployment, primarily driven by demand-side factors and unadjusted expectations.
• The expectations-augmented Phillips curve incorporates how inflation expectations shift the short-run curve. These expectations can be adaptive (backward-looking) or rational (forward-looking).
• In the long run, after expectations fully adjust, the long-run Phillips curve is vertical at the natural rate of unemployment. There is no permanent trade-off.
• Stagflation, caused by adverse supply shocks, results in high inflation and high unemployment simultaneously, demonstrating that the curve can shift to a worse position.
• Key policy takeaways are that demand management has only temporary effects on unemployment, anchoring inflation expectations is crucial for stability, and long-term unemployment reduction requires structural, not just monetary or fiscal, policies.