Determinants of Demand and Supply; Movements, Shifts, and Equilibrium

Overview: Demand, Supply, and Market Equilibrium

• Demand reflects the quantities people are willing and able to buy at a series of given prices; a change in price causes movement along the demand curve (quantity demanded changes) but does not shift the curve (demand itself remains the same).
• A change in demand shifts the entire demand curve, creating a new relationship between price and quantity demanded.
• Supply reflects how much producers are willing and able to offer for sale at each given price; a change in price causes movement along the supply curve (quantity supplied changes) but does not shift the curve (supply itself remains the same).
• A change in supply shifts the entire supply curve, creating a new relationship between price and quantity supplied.

Key Concepts: Demand vs. Quantity Demanded; Shift vs Movement

• Quantity demanded: the numeric amount consumers want to buy at a specific price on the demand curve.
• Demand: the entire willingness to buy at every price; a shift occurs due to non-price determinants.
• Movement along the demand curve: caused by a price change, holding other determinants constant.
• Shift of the demand curve: caused by a non-price determinant changing overall willingness to buy.
• Movement along the supply curve: caused by a price change, holding other determinants constant.
• Shift of the supply curve: caused by non-price determinants changing overall willingness to sell.

Determinants of Demand (non-price factors that can shift the demand curve)

• Tastes and preferences: changes can increase or decrease demand for a good.

• Income (Normal vs Inferior goods):

  • Normal goods: when income increases, demand increases. Example: luxury items, higher-quality foods.
  • Inferior goods: when income increases, demand decreases. Example: ramen noodles for college students; as income rises, demand for ramen tends to fall.

• Prices of related goods (substitutes and complements):

  • Substitutes: if the price of a substitute falls, demand for the original good falls (e.g., Diet Coke vs Diet Pepsi).
  • Complements: if the price of a complement falls, demand for the related good increases (e.g., chips and dip).

• Number of buyers: more buyers shift the demand curve to the right; fewer buyers shift it to the left.

• Expectations about future prices: if people expect prices to rise in the future, they buy more now; if they expect prices to fall, they delay purchases.

• Prices of related goods in consumption (as above) and other context-specific factors.

• Examples from the transcript:

  • Inferior good example: ramen noodles as income rises, demand for ramen may fall; as income increases (e.g., after graduation to $50,000/year), you might buy less ramen and more premium foods (e.g., T-bone steak).
  • Normal good example: T-bone steak becomes more desirable as income rises.
  • Substitutes: Diet Coke vs Diet Pepsi — if Diet Pepsi becomes cheaper, demand for Diet Coke falls.
  • Complements: chips and dip — if chips price falls (or dip becomes cheaper), people buy more chips and may buy more dip.
  • Food choices tied to income: fast food vs higher-quality dining as income changes; thrift/secondhand clothing vs new clothing as income changes (thrift stores become relatively more attractive at lower incomes).
  • Expectations about income and job prospects; e.g., graduates expecting higher future income may purchase more now.

• All determinants are discussed with a focus on real-world examples (gasoline demand, income effects, and consumption choices).

Determinants of Supply (non-price factors that can shift the supply curve)

• Resource prices (costs of inputs): land, labor, capital; higher input costs reduce supply, lower costs increase supply.

• Technology and production capabilities: advancements (e.g., fracking) can increase supply by making production cheaper or more efficient.

• Taxes and subsidies:

  • Taxes on production decrease supply (raise cost or reduce incentives).
  • Subsidies increase supply (lower effective cost or provide incentives).

• Prices of other goods in production: the opportunity to switch production to another good can alter supply of the current good (e.g., farmers choosing between crops or manufacturers reallocating production between products).

• Producer expectations about future prices: if producers expect higher prices in the future, they may restrict current supply to sell more later at higher prices; if they expect lower prices in the future, they may rush output to sell now.

• Number of sellers: more sellers increase market supply; fewer sellers decrease it.

• Weather and natural conditions: weather can impact production and thus supply (e.g., hurricanes affecting refineries, ice storms affecting oil wells). Note: weather is not typically listed as a standard determinant of supply, but it can influence production costs and capacity.

• Examples from the transcript:

  • Resource costs: higher land, labor, or capital costs reduce supply; lower costs increase supply.
  • Technology (fracking): fracking has increased oil supply by enabling more extraction.
  • Taxes and subsidies: taxes on lumber raise costs and reduce housing-related supply; subsidies for wind/solar power increase supply of those energies; removing subsidies reduces supply.
  • Production switching: farmers may shift from soybeans to corn if future prices favor corn.
  • Producer expectations: if prices are expected to be much higher next year, firms might withhold some supply now; if prices are expected to drop, they may push more supply now.
  • Number of sellers: more ice cream carts in a market increases overall supply.
  • Weather: hurricanes in the Gulf can reduce refinery output; weather can impact supply but is not a standalone determinant in the standard list.

• Notation for supply and shifts:

  • Quantity supplied is the point on the supply curve for a given price; a price change moves along the existing curve.
  • A shift in the supply curve occurs when a non-price determinant changes supply at every price.
  • Production of multiple goods and cross-commodity effects: firms can switch production to other goods, affecting the supply of a given good.

Mathematical Formulations and Models

• Demand as a function of price and determinants:
  • Quantities demanded: Qd = D(P, I, T, P{sub}, P_{comp}, N, E)
  • Where:
  • P = price of the good
  • I = income
  • T = tastes/preferences
  • P_sub = price of substitutes
  • P_comp = price of complements
  • N = number of buyers
  • E = expectations about future prices
• Supply as a function of price and determinants:
  • Quantities supplied: Qs = S(P, R, Tech, Taxes, Subsidies, P{alt}, Ep, Ns)
  • Where:
  • P = price of the good
  • R = input/resource prices (land, labor, capital)
  • Tech = technology level
  • Taxes = taxes on production
  • Subsidies = subsidies for production
  • P_alt = prices of other goods that could be produced
  • E_p = producer expectations about future prices
  • N_s = number of sellers
• Market equilibrium (where supply equals demand):
  • Qd(P^) = Qs(P^) and the corresponding price $P^$ gives equilibrium quantity Q^ = Qd(P^) = Qs(P^)
• Shifts vs movements:
  • Movement along the curve: price change with determinants held constant.
  • Shift of the curve: a non-price determinant changes the entire relationship between price and quantity.

Equilibrium, Efficiency, and the Production Possibility Context

• Market equilibrium occurs at the intersection of the demand and supply curves; at this point there is a single equilibrium price and quantity.
• Efficiency concepts linked to equilibrium:
  • Productive efficiency: firms produce goods at the lowest possible cost, on the production possibility frontier (PPF).
  • Allocative efficiency: the right quantities of goods are produced given consumer preferences and scarce resources; resources are allocated to their most valued uses.
• The lecture connects equilibrium to overall market efficiency, noting that the market system tends toward efficiency under competitive conditions.

Quick Reference: What Shifts Demand vs Supply (Summary)

• Demand shifts when:
  • Tastes/preference changes
  • Income changes (normal vs inferior goods)
  • Prices of related goods change (substitutes/complements)
  • Number of buyers changes
  • Expectations about future prices change
• Supply shifts when:
  • Resource input costs change
  • Technology changes
  • Taxes or subsidies change
  • Prices of other producible goods change (opportunity cost shifts)
  • Producer expectations about future prices change
  • Number of sellers changes
  • External factors like weather can affect production capacity/costs (not a standard determinant, but impactful)

Practical Takeaways and Study Tips

• Always distinguish between movement along a curve (due to price) and a shift of the curve (due to non-price determinants).
• For demand, remember normal vs inferior goods with income changes; use ramen vs T-bone as simple illustrations.
• For supply, remember that taxes/subsidies, technology, and input costs are major levers that shift curves; price changes move along the curve.
• Be able to explain substitutes vs complements with real-world examples (Diet Coke vs Diet Pepsi; chips and dip).
• Understand producer expectations: higher expected future prices can reduce current supply, and vice versa.
• Recognize the role of a single market’s equilibrium in achieving efficiency, and how shifts can cause surpluses or shortages until a new equilibrium is reached.

Quick Practice Scenarios (to test understanding)

• Scenario 1: Income increases in a country with gasoline consumption considered a normal good. What happens to the demand curve for gasoline? Answer: the demand curve shifts right (increase in demand).
• Scenario 2: A new technology makes refining gasoline cheaper, shifting the supply curve. What happens to the equilibrium price and quantity? Answer: supply increases; price tends to fall, quantity increases.
• Scenario 3: The price of potato chips falls, and chips and salsa are complements. What happens to the demand for salsa? Answer: demand for salsa increases (because a fall in the price of chips increases quantity demanded of chips and, as a complement, raises demand for salsa).
• Scenario 4: Expecting higher future oil prices, oil producers cut current output. What happens to the current supply? Answer: current supply decreases (shift left) due to producer expectations about future prices.

Connection to the Course and Real-World Relevance

• The determinants of demand and supply underpin policy discussions (taxes, subsidies, tariffs) and business decisions (pricing strategies, inventory management, production planning).
• Understanding the distinction between movements and shifts helps explain why policy changes don't just affect prices but can reallocate resources across industries.
• The model applies to a wide range of goods, from everyday items (gasoline, ramen) to durable goods (cars) and services, illustrating how micro-level decisions aggregate into macro-level market outcomes.

Final Clarifications from the Lecturer

• Tax on an item is a determinant of supply, not demand (in the standard model).
• A subsidy increases supply; removing a subsidy reduces supply.
• The price of the item itself determines the quantity supplied (movement along the supply curve); the determinants listed above determine shifts in the supply curve.
• Weather can impact production and supply, even if it is not a core determinant listed in every model.
• The combination of demand and supply analysis explains equilibrium and efficiency and helps interpret real-world scenarios like housing markets, energy markets, and consumer goods markets.

Answer Key (Key Takeaway from the Example Discussion)

• The current price of a commodity helps determine the quantity supplied (movement along the supply curve).
• Future price expectations, technology, input costs, taxes/subsidies, and the number of sellers shift the supply curve.
• For demand, income changes lead to normal vs inferior goods; tastes, prices of substitutes and complements, number of buyers, and expectations shift the demand curve.
• The market equilibrates at a price where quantity supplied equals quantity demanded, generating productive and allocative efficiency under appropriate competitive conditions.

Summary of Notation to Remember

• Demand function: Qd = D(P, I, T, P{sub}, P_{comp}, N, E)
• Supply function: Qs = S(P, R, Tech, Taxes, Subsidies, P{alt}, Ep, Ns)
• Equilibrium: Qd(P^) = Qs(P^) with equilibrium price P^ and quantity Q^ = Qd(P^) = Qs(P^)
• Movement along curves vs shifts of curves: price changes cause movement along the curve; non-price determinants cause shifts.