Define Economic Principles and Models
Core Concepts
AP Macroeconomics requires precise definitions of foundational principles and models. Key concepts include scarcity, opportunity cost, production possibilities curve (PPC), comparative advantage, supply and demand, circular flow, GDP, unemployment, inflation, and aggregate supply/aggregate demand (AS/AD). You must distinguish between positive (what is) and normative (what ought to be) statements, and between micro and macro topics.
Models to Know
- PPC: Shows trade-offs, efficiency, and growth. Points inside are inefficient, on the curve efficient, outside unattainable. A bowed-out shape reflects increasing opportunity cost.
- Circular Flow: Households supply factors of production and demand goods; firms demand factors and supply goods. Leakages (saving, taxes, imports) and injections (investment, government spending, exports) affect equilibrium.
- AS/AD: Short-run aggregate supply (SRAS) slopes upward due to sticky wages/prices; long-run aggregate supply (LRAS) is vertical at potential output. Demand shocks move equilibrium; supply shocks shift SRAS.
Common Traps
- Confusing a change in demand (shift) with a change in quantity demanded (movement along the curve).
- Misidentifying opportunity cost as the monetary price rather than the value of the next best alternative.
- Assuming LRAS shifts with price level; it shifts only with changes in resources or technology.
- Forgetting that GDP measures final goods and services produced within a country’s borders in a given period.
Worked Example
Suppose a country can produce either 100 units of clothing or 50 units of food. The opportunity cost of 1 unit of food is 2 units of clothing. If it currently produces 80 clothing and 10 food, it is inside its PPC (inefficient) because it could produce more of one good without less of the other.
Rule of thumb: Always label axes and curves on graphs; shifts vs. movements are the most tested distinction.