Unit 1: Basic Economic Concepts

Scarcity, Choice, and the Economic Way of Thinking

Economics is the systematic study of choice: how people, firms, and societies use their scarce productive resources to best satisfy unlimited wants. Scarcity means resources are limited relative to our wants. This does not mean we cannot have “a lot” of something; it means we cannot have everything we want all at once without giving something up. In economics, essentially all resources are treated as limited (even things that seem abundant, like clean air or fresh water, can become scarce).

Because scarcity forces trade-offs, economics focuses on how decisions are made and how incentives shape behavior.

Macroeconomics vs. microeconomics

Macroeconomics looks at the economy as a whole (the “big picture”), such as national output, inflation, unemployment, and how changes in the money supply might affect a country’s imports and exports.

Microeconomics focuses on individuals and specific markets (consumers, firms, and industries), while still recognizing the broader economic environment.

Needs, wants, and resources (factors of production)

To understand scarcity, you need to know what we are choosing with. Economists group productive resources into factors of production:

• Land (natural resources): resources created by nature, such as arable land, mineral deposits, oil and gas reserves, timber, and water.
• Labor: human effort and talent, physical and mental. Education and training can increase productivity; this improved labor is often called human capital.
• Capital (physical capital): human-made tools used to produce other goods and services, including machinery, buildings, roads, vehicles, and computers. In macroeconomics, capital is not money; it is productive equipment.
• Entrepreneurship (entrepreneurial ability): the effort, risk-taking, innovation, and know-how needed to combine the other resources into a productive venture.

Scarcity exists because these factors are limited. Even if a country has abundant land, it may still have limited skilled labor, limited capital, or limited entrepreneurship.

Trade-offs and opportunity cost: the real cost of any decision

Since resources are scarce, individuals, firms, and governments face trade-offs.

• For individuals, trade-offs show up in everyday choices such as housing, transportation, and what to buy.
• For firms, trade-offs often involve what to produce, how much to produce, and which production method to use.
• For the government, trade-offs involve competing priorities that affect citizens’ lives.

Every trade-off has an opportunity cost: the value of the next best alternative you give up when you choose something.

A key idea is that opportunity cost is not just money; it can include time, missed experiences, or the value of a forgone option.

Example (opportunity cost, wages): You have one scarce hour and can either study, work at a coffee shop for 8 per hour, or mow your uncle’s lawn for 10 per hour. If you choose to study, the opportunity cost is 10 (the best alternative you gave up).

Example (opportunity cost, next best alternative): If you spend Saturday working a shift for 120, your opportunity cost might be relaxation, time with friends, or studying. If your next best alternative was tutoring that would have paid 150, then the opportunity cost of taking the 120 shift is 150 (not the 120).

Marginal thinking: decisions are made at the margin

Most real decisions are not “all or nothing.” Economists model this using marginal analysis, which compares additional benefits and additional costs:

• Marginal benefit (MB): the additional benefit from one more unit.
• Marginal cost (MC): the additional cost from one more unit.

Decision rule:

• Do more of an activity if MB > MC.
• Do less if MB < MC.
• The efficient stopping point is where MB = MC.

Incentives: how behavior responds

An incentive is anything that motivates people to act in a certain way, such as prices, wages, taxes, subsidies, fines, and social rewards. Economics assumes people respond to incentives (not perfectly, but predictably enough to model). For example, if gasoline prices rise, driving becomes more costly, so people may carpool, drive less, or buy more fuel-efficient cars.

Models, assumptions, and ceteris paribus

Economists use models, simplified representations of reality, to clarify cause-and-effect. A crucial assumption is ceteris paribus (“all else equal”), which lets you isolate one change at a time. For example, when we say higher prices reduce quantity demanded, that is true ceteris paribus (assuming income, tastes, and other determinants do not change).

Positive vs. normative statements

Economists distinguish:

• Positive statements: descriptive, testable claims (true/false). Example: “If interest rates rise, borrowing tends to fall.”
• Normative statements: value judgments about what should be done. Example: “The government should raise the minimum wage.”

Exam Focus

• Typical question patterns:
  • Identify the opportunity cost of a choice when given multiple alternatives.
  • Decide whether a statement is positive or normative.
  • Apply marginal reasoning to determine whether an additional action should be taken based on marginal cost vs. marginal benefit.
• Common mistakes:
  • Treating opportunity cost as the money paid, instead of the next best alternative forgone.
  • Forgetting “all else equal” and mixing up a change in price with a change in some other determinant.
  • Thinking marginal analysis is about totals rather than “one more unit.”

Production Possibilities Curve (PPC): Trade-offs, Efficiency, and Growth

The production possibilities curve (PPC) shows the maximum combinations of two goods (or categories of goods) an economy can produce using its resources fully and efficiently, given current technology. It’s a key model for visualizing scarcity, trade-offs, unemployment (unused resources), and economic growth.

How to read a PPC

A PPC graph has two goods on the axes (often “consumer goods” vs. “capital goods,” or “guns” vs. “butter”).

• Points on the PPC are productively efficient: resources are fully employed and used in the least-cost way.
• Points inside the PPC are inefficient: resources are underutilized (such as unemployment) or misallocated.
• Points outside the PPC are unattainable with current resources and technology.

Moving from an interior point to the PPC can represent reducing unemployment or using existing resources more effectively. Shifting the entire PPC outward represents economic growth.

Opportunity cost on the PPC (slope and inverse)

As you move along the PPC, producing more of one good requires producing less of the other. The opportunity cost is reflected in the curve’s slope.

• The slope of the PPC measures the opportunity cost of the good on the x-axis.
• The inverse of the slope measures the opportunity cost of the good on the y-axis.

Constant vs. increasing opportunity cost (and why the PPC is usually bowed)

If opportunity cost were constant, the PPC would be a straight line. In reality, PPCs are usually bowed outward (concave to the origin), illustrating the law of increasing opportunity cost: as production of one good rises, the opportunity cost of additional units tends to rise.

This bowed shape occurs because resources are not equally suited to producing every good. As you shift more resources into producing one good, you eventually must use resources that are less compatible with that good, lowering productivity and increasing the opportunity cost.

Some discussions mention “decreasing opportunity cost,” but a PPC that implies decreasing opportunity cost is not realistic as a general pattern for economies.

Efficiency: productive vs. allocative

• Productive efficiency means producing the maximum output possible with available resources and technology; all points on the PPC are productively efficient.
• Allocative efficiency means producing the mix of goods and services that provides the most net benefit to society (the “optimal” mix). The PPC alone cannot identify the allocatively efficient point because it depends on society’s preferences and values.

A related concept is market failure, which occurs when a market fails to produce the allocatively efficient quantity.

Shifts of the PPC: growth and contraction

The PPC shifts when the economy’s productive capacity changes.

Outward shifts (economic growth) can result from:

• An increase in the quantity of resources (such as a larger labor force or more capital)
• An increase in the quality of resources (such as higher human capital)
• Technological advancements

Inward shifts reflect lost capacity (for example, war or natural disasters).

Relatedly, economic contraction is when a country’s economy shrinks, often due to reduced spending by consumers, businesses, or the government. Contractions are a normal part of the business cycle and can lead to long-term growth if managed correctly.

A classic macro trade-off: producing more capital goods today (investment in machines, factories, education) often means fewer consumer goods today, but can shift the PPC outward more in the future.

Worked example: interpreting a PPC movement

Suppose an economy produces consumer goods (C) and capital goods (K).

• If the economy is inside the PPC due to high unemployment, moving to the PPC increases both C and K because idle resources become employed.
• If the economy is already on the PPC and increases K, it must reduce C; the opportunity cost of more investment is less current consumption.

Common misconception to avoid: You cannot increase both goods while already on the PPC unless the PPC shifts outward (or you were initially inside the curve).

Opportunity cost calculation example (using changes between points)

Opportunity cost on a PPC is often computed as the ratio of what is given up to what is gained.

• The opportunity cost for guns (D):

OC_{guns} = (20-15)/(9-6) = 5/3 = 1.67

• The opportunity cost for butter (D):

OC_{butter} = (12-9)/(15-10) = 3/5 = 0.6

Exam Focus

• Typical question patterns:
  • Identify whether a point is efficient, inefficient, or unattainable on a PPC.
  • Determine whether a scenario causes a movement along the PPC (reallocation) or a shift of the PPC (growth/decline).
  • Compute or interpret opportunity cost from movements along the curve, including using slope logic.
• Common mistakes:
  • Confusing an outward shift (more capacity) with a move from inside to on the curve (better utilization).
  • Saying “technology improves” but drawing a movement along the curve rather than shifting it.
  • Treating the slope as constant even when the PPC is bowed (increasing opportunity cost).

Comparative Advantage and Gains from Trade

Trade can raise living standards because specialization based on comparative advantage can increase total output. Importantly, gains from trade can exist even if one country (or producer) is better at producing everything.

Absolute advantage vs. comparative advantage

• Absolute advantage: the ability to produce more output with the same resources (or, in input terms, to produce a unit using fewer inputs).
• Comparative advantage: the ability to produce a good at a lower opportunity cost.

Comparative advantage, not absolute advantage, determines specialization patterns that create gains from trade.

Intuition and a simple example (two producers)

Imagine a bakery and a pizza parlor that can both produce pastries and pizza crusts.

• If the bakery can produce more pastries per day than the pizza parlor, it has an absolute advantage in pastries.
• If the bakery gives up fewer crusts per pastry than the pizza parlor does, it has a comparative advantage in pastries.

In that case, specialization (bakery focuses more on pastries, pizza parlor focuses more on crusts) can increase total production, and trade can allow both to consume more than they could without specialization.

Calculating opportunity cost (the skill AP tests)

AP questions commonly require per-unit opportunity cost.

Example (two countries, two goods): In one day:

• Country A can produce 10 computers or 20 tons of wheat.
• Country B can produce 6 computers or 12 tons of wheat.

Opportunity costs:

• For Country A:
  • 1 computer costs 2 tons of wheat.
  • 1 ton of wheat costs 0.5 computer.
• For Country B:
  • 1 computer costs 2 tons of wheat.
  • 1 ton of wheat costs 0.5 computer.

Here, opportunity costs are identical, so neither has comparative advantage and specialization will not create gains.

Now change Country B: it can produce 6 computers or 18 tons of wheat.

• For Country B:
  • 1 computer costs 3 tons of wheat.
  • 1 ton of wheat costs 0.333 computers.

Then:

• Country A has comparative advantage in computers (2 wheat per computer vs. 3).
• Country B has comparative advantage in wheat (0.333 computer per ton vs. 0.5).

Output problems vs. input problems

There are two common types of comparative advantage questions:

• Output problems (given how much each country can produce):

  • Absolute advantage: the producer with the higher output.
  • Comparative advantage: compute per-unit opportunity cost using the “give up/gain” idea (what you give up divided by what you gain). The lower opportunity cost indicates comparative advantage.
  • If outputs are equal, neither has absolute advantage.

• Input problems (given how many resources each producer uses to make one unit):

  • Absolute advantage: the producer using fewer inputs (the lower number).
  • Comparative advantage: compute per-unit opportunity cost using the “gain/give up” framing appropriate for input data. The lower opportunity cost indicates comparative advantage.
  • If input requirements are equal, neither has absolute advantage.

In both cases, countries tend to export goods in which they have comparative advantage and import goods in which they do not.

Terms of trade (and when both sides benefit)

To ensure both sides gain, the trading price must lie between the two opportunity costs.

In the revised computer-wheat example:

• A’s cost of 1 computer is 2 wheat.
• B’s cost of 1 computer is 3 wheat.

A mutually beneficial trade price for 1 computer is between 2 and 3 wheat (for example, 2.5 wheat per computer).

The phrase terms of trade refers to the relative price at which two goods are exchanged internationally; it is often discussed as the ratio of a nation’s export prices to its import prices.

Exam Focus

• Typical question patterns:
  • Calculate opportunity costs and identify comparative advantage.
  • Determine whether a proposed trade price creates gains for both parties.
  • Distinguish absolute advantage from comparative advantage in word problems, including both output and input setups.
• Common mistakes:
  • Choosing comparative advantage based on who produces more (that is absolute advantage).
  • Calculating opportunity cost backward (mixing up “per unit” comparisons).
  • Thinking trade only benefits the “weaker” producer; trade can benefit both.

Demand: How Buyers Respond to Prices and Other Factors

A market is any arrangement that allows buyers and sellers to exchange. The demand model describes the relationship between a good’s price and how much consumers buy.

The law of demand

Demand is the relationship between the price of a good and the quantity consumers are willing and able to buy over a period of time.

The law of demand states: as price rises, quantity demanded falls, ceteris paribus.

This downward relationship is commonly explained by:

1. Substitution effect: as a good becomes more expensive, buyers switch toward relatively cheaper substitutes.
2. Income effect: when price rises, purchasing power falls, so consumers tend to buy less.

Demand vs. quantity demanded

This distinction is tested constantly:

• A change in the price of the good causes a change in quantity demanded (movement along the demand curve).
• A change in another factor causes a change in demand (shift of the entire demand curve).

Determinants that shift demand (INSECT)

Demand shifters are variables that cause consumers to buy more or less at every price. A useful mnemonic is INSECT:

• I = Income
  • Normal goods: demand rises when income rises.
  • Inferior goods: demand falls when income rises.
• N = Number of buyers/consumers (population and demographics)
• S = Substitutes (if the price of one rises, demand for the other rises)
• E = Expectations of future price (expect higher future prices can raise demand today)
• C = Complements (used together; if the price of one rises, demand for the other falls)
• T = Tastes and preferences (trends, advertising, habits)

Direction summary:

• Demand increases when income increases (for normal goods), number of buyers increases, the price of substitutes increases, expectations of future price increase, the price of complements decreases, or tastes shift favorably.
• Demand decreases when income decreases (for normal goods), number of buyers decreases, the price of substitutes decreases, expectations of future price decrease, the price of complements increases, or tastes shift unfavorably.

Market demand vs. individual demand

An individual demand curve shows one consumer’s behavior. A market demand curve sums all consumers at each price. If more buyers enter a market, market demand shifts right even if individual demand curves do not change.

Example: shift vs. movement

If the price of smartphones falls, that causes a movement along the demand curve: quantity demanded increases.

If incomes rise and smartphones are a normal good, that shifts demand right: at every price, consumers want more.

Exam Focus

• Typical question patterns:
  • Identify whether a scenario causes movement along demand or a shift of demand.
  • Predict the direction of a demand shift using INSECT determinants.
  • Interpret demand schedules and graphs.
• Common mistakes:
  • Confusing “demand” with “quantity demanded.”
  • Mixing up complements and substitutes (a quick check: complements move in the same direction; substitutes move in opposite directions).
  • Assuming all goods are normal goods (inferior goods are an important exception).

Supply: How Sellers Respond to Prices and Costs

Supply describes the different quantities of goods and services that producers are willing and able to sell at various prices over a period of time.

The law of supply

The law of supply states: as price rises, quantity supplied rises, ceteris paribus.

Higher prices tend to make production more profitable, and expanding output often requires using more expensive resources or paying overtime, which higher prices help cover.

Supply vs. quantity supplied

• A change in the price of the good causes a change in quantity supplied (movement along the supply curve).
• A change in another factor causes a change in supply (shift of the entire supply curve).

Quantity supplied is one point on the curve at a given price; supply is the entire curve.

Determinants that shift supply (ROTTEN)

A common mnemonic is ROTTEN:

• R = Resources (input prices): higher costs of land, labor, or capital reduce supply (shift left); lower input costs increase supply (shift right).
• O = Other good prices: if a firm can switch production, a higher price for an alternative product can reduce supply of the original good (resources shift away), and a lower alternative price can increase supply of the original good.
• T = Taxes: taxes raise per-unit costs and shift supply left; subsidies lower costs and shift supply right.
• T = Technology: improved technology lowers costs and shifts supply right.
• E = Expectations of suppliers: if producers expect higher future prices, they may hold back current supply (shift left today).
• N = Number of competitors (sellers): more sellers shift supply right; fewer sellers shift supply left.

Example: interpreting supply shifts

If a drought reduces crop yields, the supply of wheat shifts left. Even if demand is unchanged, equilibrium price tends to rise and equilibrium quantity tends to fall.

A common wording trap: if costs rise, students sometimes say “quantity supplied decreases.” Unless the good’s own price changed, this is a shift of supply, not a movement along the curve.

Exam Focus

• Typical question patterns:
  • Identify whether a scenario causes a movement along supply or a shift of supply.
  • Use ROTTEN determinants to predict supply shifts (input costs, taxes/subsidies, technology, expectations, number of sellers, other product prices).
  • Combine supply shifts with demand to predict equilibrium changes.
• Common mistakes:
  • Confusing “supply” with “quantity supplied.”
  • Forgetting that taxes/subsidies shift supply because they change costs.
  • Assuming technology affects demand instead of supply (it primarily changes productivity and costs).

Market Equilibrium: Where Supply Meets Demand

A market reaches equilibrium when the quantity buyers want to purchase equals the quantity sellers want to sell at a particular price. The equilibrium price is also called the market-clearing price.

• Equilibrium price: the price where Q_d = Q_s.
• Equilibrium quantity: the quantity bought and sold at that price.

Surplus and shortage: what pushes price to change

When the market is not at equilibrium, incentives create pressure for price adjustment:

• Surplus (excess supply): Q_s > Q_d at the current price. Sellers cut prices to reduce inventories.
• Shortage (excess demand): Q_d > Q_s at the current price. Buyers bid up prices or sellers raise prices.

Example (disequilibrium): At a price of 8, suppose quantity demanded is 100 while quantity supplied is 350. This creates a surplus and puts downward pressure on price.

Changes in equilibrium: a reliable approach

When solving equilibrium-change problems:

1. Decide whether the shock affects demand, supply, or both.
2. Decide whether it is an increase (right shift) or decrease (left shift).

Key one-shift results:

1. Demand increases, supply unchanged: price rises, quantity rises.
2. Demand decreases, supply unchanged: price falls, quantity falls.
3. Supply increases, demand unchanged: price falls, quantity rises.
4. Supply decreases, demand unchanged: price rises, quantity falls.

When both demand and supply shift

• Demand and supply both increase: quantity definitely rises; price is ambiguous.
• Demand and supply both decrease: quantity definitely falls; price is ambiguous.
• Demand increases and supply decreases: price definitely rises; quantity is ambiguous.
• Demand decreases and supply increases: price definitely falls; quantity is ambiguous.

“Ambiguous” means it depends on which shift is larger.

Worked example: equilibrium using equations

Suppose:

Q_d = 100 - 2P

Q_s = 20 + 3P

Set Q_d = Q_s:

100 - 2P = 20 + 3P

80 = 5P

P = 16

Then equilibrium quantity:

Q = 100 - 2(16) = 68

So equilibrium is P = 16 and Q = 68. A good habit is to plug the price into both equations to verify the same quantity results.

Exam Focus

• Typical question patterns:
  • Given a graph or story, identify surplus/shortage and predict how price changes.
  • Determine the new equilibrium after a shift in supply and/or demand.
  • Solve for equilibrium price and quantity using demand and supply equations.
• Common mistakes:
  • Labeling the result of a rightward shift as a movement along the curve.
  • Forgetting which curve shifts when given a cost shock (supply) versus a taste/income shock (demand).
  • Assuming price and quantity always move in the same direction.

The Circular Flow Model: Connecting Markets to the Whole Economy

Macroeconomics is about how markets connect across the whole economy. The circular flow model shows how resources, goods and services, and money payments move between households and firms through markets. This framework is a “map” for later topics like GDP, unemployment, inflation, and policy.

The two main decision-makers: households and firms

• Households own factors of production (labor, land, capital, entrepreneurship) and supply them to firms.
• Firms demand factors of production to produce goods and services.

The two core markets

1. Factor market (resource market)

   • Households supply labor, land, capital, and entrepreneurship.
   • Firms demand these inputs.
   • Money flows to households as wages, rent, interest, and profit.

2. Product market (goods and services market)

   • Firms supply goods and services.
   • Households demand goods and services.
   • Money flows to firms as consumer spending.

Real flows vs. money flows

• Real flows: physical resources and goods/services.
• Money flows: payments for resources and goods/services.

For example, labor is a real flow; wages are a money flow.

Extensions: government, financial sector, and foreign sector

More complete circular flow diagrams also include:

• Government: collects taxes and purchases goods/services.
• Financial sector: channels saving into investment (banks and financial markets).
• Foreign sector: imports and exports connect the domestic economy to the world.

Exam Focus

• Typical question patterns:
  • Identify which market (factor vs. product) a transaction belongs to.
  • Classify flows as real or monetary.
  • Reason about how a change (taxes, wages, spending) affects households vs. firms.
• Common mistakes:
  • Placing households as sellers in the product market (firms sell goods; households buy them).
  • Calling “money” a factor of production (capital is machinery/tools, not cash).
  • Mixing up wages (money flow) with labor (real flow).

Market Efficiency, Surplus, and Government Intervention (Price Controls)

Market equilibrium predicts where the market tends to settle, but economics also evaluates whether that outcome is efficient, meaning resources are allocated to maximize the benefits society receives given scarcity.

Consumer surplus and producer surplus

Surplus measures the gains from voluntary exchange.

• Consumer surplus (CS): the difference between what consumers are willing to pay and what they actually pay.
• Producer surplus (PS): the difference between the price producers receive and the minimum price they would accept to sell.

On a supply-and-demand graph:

• Consumer surplus is the area below demand and above price, up to the quantity traded.
• Producer surplus is the area above supply and below price, up to the quantity traded.

Total surplus is:

TS = CS + PS

In the basic competitive market model, equilibrium tends to maximize total surplus.

Price controls: ceilings and floors

A price control is a legal minimum or maximum price.

• A price ceiling is a maximum legal price.
• A price floor is a minimum legal price.

A price control only changes outcomes if it is binding.

Price ceilings (maximum prices)

A price ceiling is binding if it is set below equilibrium. A binding ceiling causes a shortage because it increases quantity demanded and decreases quantity supplied.

Real-world examples include rent controls or emergency price caps.

Shortages can create:

• Non-price rationing (waiting lines, favoritism)
• Reduced product quality
• Black markets

A key insight is that a price ceiling does not automatically help all consumers; some may benefit from lower prices, while others lose access due to the shortage.

Price floors (minimum prices)

A price floor is binding if it is set above equilibrium. A binding floor causes a surplus because quantity supplied rises and quantity demanded falls.

Examples include minimum wages (in labor markets) and some agricultural price supports.

Surpluses can create:

• Unsold inventories
• Pressure for the government to purchase excess output
• Misallocation of resources (too many resources drawn into the price-supported good)

Deadweight loss: lost gains from trade

When price controls prevent mutually beneficial trades that would have occurred at equilibrium, total surplus falls. The reduction in total surplus is deadweight loss (DWL): gains from trade that no one receives. The logic is that when fewer units are traded than the efficient equilibrium quantity, some buyers and sellers who would have both benefited cannot trade.

Simple example (shortage under a ceiling)

Suppose the equilibrium price for concert tickets is 100. A binding price ceiling is imposed at 60.

• At 60, more people want tickets (higher Q_d).
• At 60, fewer tickets are offered (lower Q_s).
• A shortage results, requiring some rationing method.

Even if the goal is fairness, the outcome can include inefficiency (missed trades) and alternative allocation methods.

Exam Focus

• Typical question patterns:
  • Identify whether a price ceiling/floor is binding and predict surplus or shortage.
  • Determine changes in price and quantity traded when a control is imposed.
  • Use CS, PS, and TS qualitatively to explain who gains and who loses.
• Common mistakes:
  • Saying “price ceilings cause surpluses” or “price floors cause shortages” (it is the opposite when binding).
  • Forgetting that a price control only matters if it is binding.
  • Assuming lower prices always increase welfare (they can reduce total surplus if they prevent trades).