Extensions of Demand and Supply Analysis

Shifts in Demand and in Supply

  • Figure 4-1 illustrates how shifts in demand and/or supply alter equilibrium price and quantity. Key notation often used in these diagrams includes:

    • D1, D2: initial and new demand curves
    • S: initial supply curve (and S1, S2 for alternate panels when shown)
    • E1, E2, E3: initial and new equilibrium points
    • P1, P2, P3: prices at respective equilibria
    • Q1, Q2, Q3: quantities at respective equilibria

  • Panel (a): Increase in Demand (driven by an increase in preferences)

    • Demand shifts right from D1 to D2 while supply S remains fixed.
    • Equilibrium moves from E1 at price P1 and quantity Q1 to E2 at price P2 and quantity Q2.
    • Result: higher price and higher quantity in the market for the good (holding other factors constant).
    • Conceptual takeaway: non-price determinants (here, preferences) shift the demand curve, altering market outcomes without any change in the price mechanism itself.

  • Panel (b): Decrease in income for a normal good (as stated: “decrease in income and it is a normal good”)

    • With a normal good, a decrease in income reduces consumers’ purchasing power, shifting the demand curve left (decrease in demand).
    • Resulting change: lower equilibrium price and lower equilibrium quantity, all else equal.
    • Note: for a normal good, income and demand move in the same direction; a decrease in income causes a fall in demand, not an increase.

  • Panel (c): Increase in Supply (caused by a decrease in an input price)

    • Supply shifts right from S1 to S2 while demand D remains the same.
    • Equilibrium moves from E1 to E2 with a lower price (P2 < P1) and higher quantity (Q2 > Q1).
    • Summary: a rise in supply reduces price and increases quantity in equilibrium.

  • Panel (d): Decrease in Supply (caused by a decrease in subsidies)

    • Supply shifts left from S1 to S3 (or similar leftward shift depending on labeling) as subsidies are reduced.
    • Equilibrium moves to E3, with a higher price (P3 > P1) and lower quantity (Q3 < Q1).
    • Interpretation: reductions in subsidies effectively decrease supply capability or increase marginal costs for producers, shifting the curve left and raising price.

  • Summary of demand-side effects (Slide 4-6):

    • Increases in demand increase equilibrium price and quantity.
    • Decreases in demand decrease equilibrium price and quantity.

  • Summary of supply-side effects (Slide 4-7):

    • Increases in supply decrease equilibrium price and increase equilibrium quantity.
    • Decreases in supply increase equilibrium price and decrease equilibrium quantity.

  • Simultaneous shifts in both demand and supply (Slide 4-8):

    • When both curves shift at the same time, opposing pressures create a conflicting effect on price or quantity.
    • The resulting outcome depends on the magnitudes of the shifts for each curve.
    • Either equilibrium price or equilibrium quantity may be indeterminate in the combined scenario.

  • Practical classroom approach (Slides 4-9 to 4-10):

    • When both demand and supply increase: price change is indeterminate, but quantity tends to increase.
    • When both demand and supply decrease: price change is indeterminate, but quantity tends to decrease.
    • When one curve shifts while the other shifts in the opposite direction:
    • If demand increases and supply decreases: price will rise; change in quantity is indeterminate.
    • If demand decreases and supply increases: price will fall; change in quantity is indeterminate.

  • Government-imposed price controls (Slide 4-11):

    • Price Controls: government-mandated minimum or maximum prices.
    • Price Ceiling: a legal maximum price.
    • Price Floor: a legal minimum price.
    • Common examples and consequences: price ceilings can create black markets (e.g., rent control); price floors can create surplus (e.g., minimum wage or agricultural price supports).

  • How a price ceiling creates black markets (Slide 4-12):

    • In a graph, a price ceiling set below the market-clearing price creates a shortage: quantity demanded exceeds quantity supplied at the ceiling.
    • Structural features shown in the diagram include the presence of an implicit supply schedule and a shortage.
    • Visual intuition: the ceiling binds the price, preventing the market from clearing at equilibrium, leading to non-price rationing and potential black markets.

  • Effects of price ceilings (Slide 4-13):

    • If the price ceiling is set below the equilibrium price, a shortage arises.
    • Shortages can lead to non-price rationing devices (e.g., queues, first-come-first-served) and black markets where trades occur at prices above the ceiling.

  • Effects of price floors (Slide 4-14):

    • If the price floor is set above the market price, a surplus results (excess supply).
    • Price floors can take forms such as government-imposed price supports or minimum wage laws.

  • Connections to real-world policy and market outcomes:

    • Price ceilings (rent control) aim to keep housing affordable but tend to reduce the quantity of rental housing supplied and can produce shortages and non-price allocation mechanisms.
    • Price floors (minimum wage) aim to raise earnings for workers but can lead to excess supply of labor (unemployed workers) or reduced hiring if set too high.

  • Quick mathematical reference (conceptual):

    • Market equilibrium condition: Q<em>d(P)=Q</em>s(P)Q<em>d(P) = Q</em>s(P)
    • A shift in demand by ΔD or in supply by ΔS changes the inverse supply/demand functions and hence the equilibrium price P* and quantity Q* according to the new intersection point of the curves.
    • Directional rules (summary):
    • If demand shifts right (increase in demand) with supply constant: P↑, Q↑.
    • If demand shifts left (decrease in demand) with supply constant: P↓, Q↓.
    • If supply shifts right (increase in supply) with demand constant: P↓, Q↑.
    • If supply shifts left (decrease in supply) with demand constant: P↑, Q↓.

  • Quick recap of notational conventions used in the figures:

    • D1, D2 denote initial and new demand curves; S1, S2 denote initial and new supply curves where shown; E1, E2, E3 denote corresponding equilibria; P1, P2, P3 denote prices at equilibria; Q1, Q2, Q3 denote quantities at equilibria.

  • Practical study tip:

    • When solving problems with simultaneous shifts, first identify the direction of each shift, then reason about possible magnitudes to determine whether price or quantity will be indeterminate. Use graphical sketches to validate the intuition.

  • Note on semantic consistency:

    • For a normal good, a decrease in income reduces demand (shift left). If the transcript’s Panel (b) is labeled as a decrease in income while still describing an increase in demand, remember the underlying economic principle: for normal goods, lower income reduces demand; for inferior goods, lower income would increase demand. The panel text suggests a decrease in income with a normal good, which aligns with the standard result (demand shifts left).