Microeconomics Study Guide: Demand, Supply, Market Equilibrium, and Market Interventions

Chapter 3: Demand, Supply, and Market Equilibrium

Supply Shifters

The supply curve shows the relationship between the price of a good and the quantity supplied. Several factors can shift the supply curve, changing the quantity supplied at every price.

• Prices of Inputs: An increase in input prices (e.g., labor, raw materials) raises production costs, shifting supply left (decrease). A decrease shifts supply right (increase).

• Technological Change: Improvements in technology lower production costs, shifting supply right.

• Prices of Related Goods in Production: If a firm can produce multiple goods, a rise in the price of one may shift supply of the other.

• Number of Firms in the Market: More firms increase supply (shift right); fewer firms decrease supply (shift left).

• Expected Future Prices: If prices are expected to rise, firms may decrease current supply (shift left).

• Natural Disasters and Pandemics: These events can disrupt production, shifting supply left.

Example: A new technology reduces the cost of producing smartphones, shifting the supply curve to the right and lowering equilibrium price.

Graphical Practice: When supply shifts right, equilibrium price falls and equilibrium quantity rises. When supply shifts left, price rises and quantity falls.

Substitutes and Complements

Substitutes and complements describe relationships between goods in consumer demand.

• Substitutes: Goods where a rise in the price of one increases demand for the other (e.g., tea and coffee).

• Complements: Goods where a rise in the price of one decreases demand for the other (e.g., printers and ink cartridges).

Example: If the price of coffee rises, demand for tea (a substitute) increases.

Normal and Inferior Goods

Goods are classified based on how demand responds to changes in income.

• Normal Goods: Demand increases as income rises (e.g., organic food).

• Inferior Goods: Demand decreases as income rises (e.g., instant noodles).

Example: When income rises, demand for restaurant meals (normal good) increases, while demand for bus rides (inferior good) may decrease.

Double Shifters

Sometimes both supply and demand shift simultaneously, making the effect on equilibrium price or quantity ambiguous.

• Example: New technology (supply right) and increased consumer preference (demand right) both shift curves right. Quantity will definitely rise, but the effect on price depends on the relative magnitude of shifts.

• Certainty vs. Ambiguity: If both curves shift in the same direction, the effect on quantity is certain; price is ambiguous unless one shift dominates.

Law of Demand

The law of demand states that, all else equal, as the price of a good falls, the quantity demanded rises, and vice versa.

• Change in Quantity Demanded: Movement along the demand curve due to price change.

• Change in Demand: Shift of the entire demand curve due to factors like income, tastes, or prices of related goods.

Example: A decrease in the price of apples leads to a higher quantity demanded (movement along the curve).

Market Equilibrium and Adjustments

Market equilibrium occurs where quantity demanded equals quantity supplied. If the market is not in equilibrium, price adjusts.

• Surplus (Excess Supply): Occurs when price is above equilibrium; leads to downward pressure on price.

• Shortage (Excess Demand): Occurs when price is below equilibrium; leads to upward pressure on price.

Example: If the price of bread is set too high, bakeries have unsold bread (surplus), and prices fall.

Demand and Supply as Marginal Curves

The demand curve represents marginal benefit (MB) to consumers; the supply curve represents marginal cost (MC) to producers. Efficiency occurs at their intersection.

• Efficiency: The market is efficient when MB = MC at the equilibrium quantity.

Example: At equilibrium, the last unit traded provides equal benefit to consumers and cost to producers.

Demand Shifters

Several factors can shift the demand curve, changing the quantity demanded at every price.

• Tastes and Preferences: Changes in consumer preferences can increase or decrease demand.

• Income Changes: Affect demand for normal and inferior goods.

• Prices of Related Goods: Substitutes and complements affect demand.

• Expectations about the Future: If consumers expect prices to rise, current demand may increase.

• Market Size: More buyers increase demand; fewer buyers decrease demand.

Chapter 4: Market Interventions and Efficiency

Price Ceilings and Price Floors

Governments sometimes set legal maximum (ceiling) or minimum (floor) prices. These interventions can affect market outcomes.

• Price Ceiling: Maximum legal price (e.g., rent control). Binding if set below equilibrium price.

• Price Floor: Minimum legal price (e.g., minimum wage). Binding if set above equilibrium price.

• Effects: Binding ceilings cause shortages; binding floors cause surpluses.

Example: A binding rent ceiling leads to apartment shortages.

Effects on Surplus and Deadweight Loss

• Consumer Surplus (CS): May increase or decrease depending on intervention.

• Producer Surplus (PS): Usually decreases with ceilings, may increase with floors.

• Deadweight Loss (DWL): Represents lost total surplus due to inefficiency.

Graphical Practice: Identify areas of CS, PS, and DWL before and after intervention.

Taxes

Taxes affect market equilibrium and efficiency. The burden (tax incidence) depends on elasticity, not who the tax is levied on.

• Tax Incidence: The division of tax burden between buyers and sellers depends on relative elasticities.

• Per-Unit Tax: Shifts supply curve vertically by the amount of the tax.

• Effects: Reduces equilibrium quantity, creates DWL, and generates tax revenue.

Example: A $1 per-unit tax on cigarettes shifts supply left; both buyers and sellers share the burden.

Key Formulas:

• Tax Revenue: $\text{Tax Revenue} = \text{Tax} \times \text{Quantity Sold}$

• Deadweight Loss: $\text{DWL} = \frac{1}{2} \times \text{Tax} \times (\text{Quantity Before Tax} - \text{Quantity After Tax})$

Consumer Surplus

Consumer surplus measures the benefit consumers receive from purchasing a good at a price lower than their willingness to pay.

• Definition: $\text{CS} = \text{Willingness to Pay} - \text{Actual Price}$

• Calculation: For a group, sum individual surpluses.

Example: If a consumer is willing to pay $10 for a book but buys it for $7, CS = $3.

Economic Efficiency

Efficiency occurs when resources are allocated so that marginal benefit equals marginal cost at the last unit traded.

• Interventions: Price ceilings, floors, and taxes move the market away from efficiency, creating DWL.

• Graph Practice: Label CS, PS, and DWL before and after an intervention.

Example: A tax reduces quantity traded, creating DWL and reducing total surplus.

Summary Table: Effects of Market Interventions

Intervention	Binding Condition	Effect on Price	Effect on Quantity	Consumer Surplus	Producer Surplus	Deadweight Loss
Price Ceiling	Below equilibrium price	Lower	Lower	May increase for some, decrease overall	Decrease	Yes
Price Floor	Above equilibrium price	Higher	Lower	Decrease	May increase for some, decrease overall	Yes
Tax	Any per-unit tax	Buyers pay more, sellers receive less	Lower	Decrease	Decrease	Yes

Additional info: Academic context and formulas were added to clarify calculation and effects of taxes, surplus, and deadweight loss.