菲利普斯曲线 — AP 宏观经济学
1. 菲利普斯曲线的核心定义与框架 ★★☆☆☆ ⏱ 3 min
菲利普斯曲线是描述经济体通胀率与失业率之间关系的核心宏观经济学模型。该关系最初由A.W.菲利普斯提出，后经萨缪尔森、索洛、弗里德曼和菲尔普斯改编，是AP宏观经济学选择题和简答题的常考考点。
标准模型将失业率（$u$）放在水平横轴，通胀率（$\pi$）放在垂直纵轴。它与AD-AS模型直接相关：推动经济体沿短期总供给（SRAS）曲线移动的总需求变动，对应着沿短期菲利普斯曲线的移动；而导致SRAS平移的变动会导致短期菲利普斯曲线平移。该模型帮助政策制定者评估货币和财政政策的短期权衡取舍。
2. 短期菲利普斯曲线（SRPC） ★★★☆☆ ⏱ 4 min
短期菲利普斯曲线（SRPC）说明了短期内（名义工资和通胀预期固定时）通胀与失业之间存在反向关系。这种反向关系直接来自AD-AS模型：总需求增加会提高产出和就业水平（降低失业），同时推高价格水平（提高通胀），而总需求减少则产生相反的效果。
\pi = \pi^e - \alpha(u - u_n)
Where $\pi$ = actual inflation rate, $\pi^e$ = expected inflation rate, $u$ = actual unemployment rate, $u_n$ = natural rate of unemployment, and $\alpha$ is a positive constant measuring how responsive inflation is to deviations of unemployment from the natural rate.
Only changes to expected inflation or supply shocks shift the SRPC. An increase in expected inflation or a negative supply shock (e.g., an oil price spike) shifts the SRPC upward/right, leading to higher inflation and higher unemployment at every level of actual unemployment. A decrease in expected inflation or a positive supply shock shifts it downward/left. Changes in aggregate demand only cause movements along a fixed SRPC.
Exam tip: 如果AP简答题要求你绘制SRPC，一定要明确标注坐标轴才能得分：横轴是失业率，纵轴是通胀率——颠倒坐标轴是该考点最常见的可避免错误。
3. Long-Run Phillips Curve (LRPC) ★★★☆☆ ⏱ 3 min
The Long-Run Phillips Curve (LRPC) describes the relationship between inflation and unemployment when all prices and expectations have fully adjusted. In the long run, workers and firms update their inflation expectations to match actual inflation, so nominal wages adjust to changes in the price level. This means there is no permanent tradeoff between inflation and unemployment in the long run: unemployment always returns to the natural rate of unemployment ($u_n$) regardless of the long-run inflation rate.
As a result, the LRPC is a vertical line at the natural rate of unemployment. This matches the vertical long-run aggregate supply (LRAS) curve in the AD-AS model: LRAS is vertical at potential output, which corresponds to the natural rate of unemployment, so any shift in LRAS leads to an identical direction shift in LRPC. Only changes to the natural rate of unemployment shift the LRPC: if structural unemployment rises from automation, $u_n$ increases, and LRPC shifts right; if job training reduces frictional unemployment, $u_n$ falls, and LRPC shifts left.
Exam tip: Always remember that the LRPC sits at the same unemployment rate that corresponds to potential output on the AD-AS model. If a question says potential output increases, that means $u_n$ falls, so LRPC shifts left.
4. Distinguishing Movements vs. Shifts of Curves ★★★★☆ ⏱ 3 min
A core AP exam skill is correctly identifying whether a given economic shock causes a movement along the SRPC, a shift of the SRPC, or a shift of the LRPC. Three simple rules apply to all exam problems: (1) Only changes in aggregate demand cause movements along a fixed SRPC; (2) Only changes in expected inflation or supply shocks shift the SRPC; (3) Only changes to the natural rate of unemployment shift the LRPC.
Exam tip: If a problem mentions "stagflation" (higher inflation + higher unemployment), this is always caused by a rightward shift of the SRPC, not a movement along the SRPC from a demand change.
5. AP-Style Concept Check ★★★★☆ ⏱ 2 min
Common Pitfalls
Why: Students confuse the short-run inverse relationship with the long-run adjustment of expectations
Why: Students mix up AD changes (which move along SRAS/SRPC) and SRAS changes (which shift SRAS/SRPC)
Why: Students get used to AD-AS where price is vertical, but mix up variable placement for the Phillips Curve
Why: Students assume any change that shifts SRPC also shifts LRPC
Why: Students confuse demand and supply shocks, assuming all inflation increases come from higher AD
Why: Students match the direction of LRAS shift directly to LRPC without linking output to unemployment