Demand and PPC: Key Concepts

Market

A market is where buyers and sellers come together to exchange goods and services. Markets can be physical or online, and include product markets, factor (e.g., labor) markets, stock markets, and international financial markets. Core ideas in market theory are demand and supply.

Demand

Demand is the quantity of a good or service that consumers are willing and able to purchase at different prices in a given time period. Effective demand requires both willingness and the financial means to buy. The Law of Demand states that, ceteris paribus, as price falls, the quantity demanded rises (the demand curve slopes downward). This relationship can be shown via a demand schedule or a demand curve.

The Law of Demand and the Demand Curve

A downward-sloping demand curve reflects the tendency for consumers to buy more as price decreases. A change in the price of the good causes a movement along the existing demand curve (a change in quantity demanded). Changes in other determinants cause the entire demand curve to shift to the left or right (a change in demand).

Movement vs. Shift of the Demand Curve

  • Movement along the curve: caused by a change in the price of the good itself.
  • Shift of the curve: caused by non-price determinants of demand (income, prices of related goods, tastes, expectations, number of buyers). When these determinants change, demand at every price changes.

Non-price Determinants of Demand

Key determinants and typical directional effects:

  • Income
    • Normal goods: demand increases with income. Demanded quantity shifts right; rac{dD}{dY} > 0.
    • Inferior goods: demand decreases with income. Demanded quantity shifts left; rac{dD}{dY} < 0\,.
  • Prices of related goods
    • Substitutes: if the price of one good falls, demand for the substitute falls (and the other substitute’s curve shifts left); conversely, a price rise in a substitute shifts its own demand right.
    • Complements: a fall in the price of one good increases the demand for its complement (demand curves for the two goods shift right together); a price rise in one reduces demand for its complement.
    • Unrelated goods: no systematic effect on each other.
  • Tastes and preferences: favorable changes increase demand (curve shifts right); unfavorable changes decrease demand (shifts left).
  • Future price expectations: if buyers expect higher prices later, they buy now (demand shifts right); if they expect lower prices, they delay (demand shifts left).
  • Number of buyers: more buyers shift demand to the right; fewer buyers shift it left.

Market Demand and Individual Demand

Market demand is the horizontal sum of individual demands: D{ ext{market}}(P) = \sum{i} D_i(P). Each individual demand curve obeys the Law of Demand; summing them gives the market demand curve.

Veblen Goods (Exceptions to the Law of Demand)

Some high-status goods (Veblen goods) may see quantity demanded rise as price rises, due to snob value or conspicuous consumption. This is an exception to the usual downward-sloping demand.

Demand for Goods vs. Market Demand – Example Concepts

  • The distinction between a movement along a demand curve (price change) and a shift of the demand curve (non-price determinants) is crucial for analysis.

Summary Concepts for Quick Recall

  • Demand = quantity willing and able to buy at various prices in a time period; effective demand requires purchasing power.
  • Law of Demand: rac{dQ_d}{dP} < 0 ext{ (ceteris paribus)}.
  • Non-price determinants shift the demand curve; price changes cause movements along the curve.
  • Normal vs inferior goods: rac{dD}{dY} > 0 for normal goods; rac{dD}{dY} < 0 for inferior goods.
  • Substitutes: price drop in one reduces demand for the other; Complements: price drop in one increases demand for the other.
  • Market demand is the horizontal sum of individual demands: D{ ext{market}}(P) = \sum{i} D_i(P).
  • Veblen goods illustrate that some goods may exhibit upward-sloping demand at high prices due to social signaling.

Production Possibility Curve (PPC)

PPC Basics

The Production Possibility Curve shows the maximum feasible combinations of two goods an economy can produce with fixed resources and technology, assuming full and efficient use of resources. It illustrates trade-offs and opportunity costs.

Opportunity Cost and the PPC

  • Opportunity Cost is the value of the next best alternative foregone when choosing a production mix. It is given by the slope of the PPC.
    • If producing more of good A requires sacrificing some of good B, the OC of one more unit of A is the amount of B forgone, and vice versa.
    • Example (chairs and tables): if 1 table requires 2 chairs, then the OC of 1 table is 2 chairs, and the OC of 1 chair is 1/2 table. Symbolically, OC = \frac{\Delta\text{chairs}}{\Delta\text{tables}} (negative slope on the frontier).

Points on, Inside, and Outside the PPC

  • On the curve: full employment and efficient use of resources.
  • Inside the curve: unemployment or underutilized resources.
  • Outside the curve: unattainable with current resources and technology.

Growth and Opportunity Cost

  • Economic growth/outward shift of the PPC occurs with technological progress or an increase in resources.
  • The traditional PPC assumes a constant OC between goods; in reality, OC often increases as more of one good is produced, leading to a concave (bowed-out) PPC shape.

Key PPC Implications

  • The PPC visualizes trade-offs, allocation efficiency, and opportunity costs.
  • Decisions about resource allocation involve choosing points on the frontier, inside the frontier when resources are underutilized, or investing to shift the frontier outward.