Chapter 4 Notes – Economic Efficiency, Price Controls, and Taxes

4.1 Consumer Surplus and Producer Surplus

• Surplus = benefit that remains above what is used/needed; economists interpret as net gain from market transactions.
• Consumer Surplus (CS)
  • $CS =\text{the difference between the highest price a consumer is willing to pay and the actual price paid}$
  • Visual = area below the demand curve and above market price.
• Producer Surplus (PS)
  • $PS =\text{the difference between the lowest price a firm would accept (its marginal cost) and the price it actually receives}$
  • Visual = area above the supply curve and below market price.
• Marginal Benefit (MB) = additional benefit from consuming one more unit; traced by a demand curve.
• Marginal Cost (MC) = additional cost of producing one more unit; traced by a supply curve.

Measuring Surplus: Chai-Tea Example

• 4 buyers: Theresa ($6), Tom ($5), Terri ($4), Tim ($3.00) represent max WTP.
• At $P = \$3.50$, buyers: Theresa ($2.50 CS), Tom ($1.50 CS), Terri ($0.50 CS) ⇒ Rectangles A, B, C.
  • CS = sum of rectangles = total shaded area between demand curve and price.
• If price falls to $\$3.00$, each participating buyer gains extra $\$0.50$ CS, Tim becomes indifferent.
• With many consumers, demand approximates a straight line; CS still area under D above P (Figure 4.3 at $P = \$2.00$).

Apply the Concept – Consumer Surplus from Uber

• Economists estimated the demand curve using 111 million rides (NYC, SF, CHI, LA; 2015).
• Avg ride price $= \$13.30$; area under demand above price gives aggregate CS → quantifies rider benefit.

Producer Surplus: Heavenly Tea Example

• At $P = \$2.00$:
  • Cup 1: MC = \$1.25 → PS = \$0.75 (Rect A).
  • Cup 2: MC = \$1.50 → PS = \$0.50 (Rect B).
  • Cup 3: MC = \$1.75 → PS = \$0.25 (Rect C).
• Total PS = sum of individual areas = area above supply curve below price for all units sold.

What Surplus Measures

• $CS = \text{Total Benefit} - \text{Total Expenditure}$
• $PS = \text{Total Revenue} - \text{Total Variable Cost}$
• Both represent net—not gross—benefits to market participants.

4.2 Efficiency of Competitive Markets

• Two equivalent definitions of market efficiency:
  1. All trades where $MB \ge MC$ occur and none where MB < MC.
  2. Economic surplus $\big( CS + PS \big)$ is maximized.
• Competitive equilibrium (E): intersection of D (MB) & S (MC); here $MB = MC$ for last unit.
• If quantity < E → unexploited gains: MB > MC.
• If quantity > E → overproduction: MC > MB.
• Deadweight Loss (DWL) = reduction in econ. surplus from non-equilibrium outcome.
  • Zero at competitive equilibrium; positive whenever price/quantity deviates.

Example of DWL

• Price rises from $\$2.00$ to $\$2.20$ for chai tea:
  • $CS$ shrinks from A+B+C to A.
  • $PS$ grows from D+E to B+D.
  • DWL = C + E → shaded triangles (lost gains).

Definition: Economic Efficiency

• Occurs when $MB = MC$ for last unit AND $CS + PS$ at maximum.

4.3 Government Intervention – Price Floors & Ceilings

• Price Ceiling: legally set $P_{max}$ sellers may charge (e.g., rent control).
• Price Floor: legally set $P_{min}$ sellers must receive (e.g., minimum wage, farm supports).
• U.S. examples: minimum wage, rent controls in NYC/SF, agricultural price supports.

Price Floor – Wheat Market (Figure 4.8)

• Competitive E: $P^{<em>}=\$6.50$, $Q^{</em>}=2.0\text{ billion bu}$.
• Government floor $P_f = \$8.00$ ⇒ Quantity traded drops to 1.8 billion bu.
  • Transfer: Area A (consumer → producer).
  • DWL: Areas B + C.
• If farmers mis-forecast demand, they might produce 2.2 billion bu → surplus of 0.4 billion.
• Labor market analogy: minimum wage may reduce low-skill employment ⇒ DWL.

Price Ceiling – Rent Control (Figure 4.9)

• No control: $P^{<em>}=\$2{,}500$, $Q^{</em>}=2{,}000{,}000\text{ apartments}$.
• Ceiling $P<em>c = \$1{,}500$: • $Q</em>s = 1{,}900{,}000$
  • $Q_d = 2{,}100{,}000$
  • Shortage = 200,000 units.
  • Transfer: Producer surplus rectangle A shifts to renters.
  • DWL = triangles B + C (lost apartments not rented).
• Consequences: illicit markets, Airbnb pivot; adds risk, removes legal protections, partially reduces DWL.

Overall Results of Price Controls

• Some gain, some lose, total surplus falls → DWL inevitable.
• Positive analysis shows inefficiency; normative judgment depends on equity goals.

Case Studies & Illustrations

• Venezuela food riots & U.S. taxi medallion decline both stem from attempts to alter prices; highlight adverse effects of distortions.
• Price gouging during Covid-19: sanitizer jumped from $\$9.95$ → $\$99.95$ online.
  • Short-run: price at Pt A benefits sellers.
  • Medium-run: supply expands, $P$ falls to $\$5.99$, quantity ↑ to $Q_3$.
  • Long-run: output increases, $P$ returns ≈ $\$3.99$ if MC returns.
  • Anti-gouging law would freeze high price but block supply expansion ⇒ persistent shortage.

4.4 Taxes – Economic Effects

• Focus on per-unit (specific) taxes; e.g., U.S. federal gasoline excise $= 18.4¢/\text{gal}$.

Cigarette Tax Example (Figure 4.10)

• Pre-tax E: $P=\$6.00$, $Q=4\text{ billion packs}$.
• Tax $t = \$1.00/\text{pack}$ shifts S up vertically by $t$.
• New E: $Q=3.7\text{ billion}$.
  • Price consumers pay $P<em>b = \$6.90$. • Price producers get $P</em>s = P_b - t = \$5.90$.
  • Tax revenue = green rectangle = $t \times Q = \$1.0 \times 3.7\text{ billion}$.
  • CS & PS fall; part converts to revenue, part to DWL (yellow area).

Excess Burden & Tax Efficiency

• Excess burden = DWL of a tax.
• Efficient tax: small excess burden relative to revenue raised.

Tax Incidence Principles

• Incidence = actual burden split between buyers and sellers; unrelated to statutory obligation.
• Determined by elasticities (slopes) of D & S.
  • Steep (inelastic) side bears more burden.

Gasoline 10¢ Tax (Figure 4.11–4.12)

• Without tax: $P = \$2.50$, $Q = 144\text{ billion gal}$.
• Tax shifts S up: consumers pay $\$2.58$, sellers receive $\$2.48$.
  • Buyers pay 8¢; sellers 2¢ → 80 % / 20 % split.
• Same split even if legal duty is on buyers (Figure 4.12).

Social Security (FICA) Tax (Apply the Concept)

• Total rate 15.3 % (split 7.65 % each by statute).
• Labor supply more inelastic than labor demand ⇒ workers bear most of burden regardless of statutory split.
• Demonstrated with hypothetical $t = \$1.00/\text{hr}$; diagrams show wages fall almost by full $1.

Appendix – Quantitative D&S Analysis (NYC Apartments)

• Demand: $Q_D = 2{,}500 - 0.5P$ (illustrative; actual numbers omitted in slide text)
• Supply: $Q_S = -500 + 0.75P$
• Equilibrium: $Q<em>D = Q</em>S$ → solve simultaneous equations.
  • Derived $P^{<em>}, Q^{</em>}$ (slide shows method but not final figures).
• Surplus Calculations:
  • CS = area of triangle under D above $P^{<em>}$. • PS = area of triangle above S below $P^{</em>}$.
• Imposing ceiling $P_c = \$1{,}500$:
  • Rented quantity falls to 950,000.
  • Deadweight loss = $\$1{,}495\text{ million}$ (B + C).
  • CS rises slightly (gain A – loss B) to $\$2,636\text{ million}$.
  • PS plunges to $\$347\text{ million}$.
  • Summary table (values in millions):
  – Competitive: $CS = 2{,}531$, $PS = 1{,}947$, $DWL = 0$.
  – Rent control: $CS = 2{,}636$, $PS = 347$, $DWL = 1{,}495$.

Ethical & Philosophical Notes

• Price controls can be justified on distributional/equity grounds—normative choice.
• Efficiency analysis (positive) reveals cost in lost surplus but does not dictate policy.
• Pandemic price-gouging debate balances short-run fairness vs. long-run supply incentives.

Connections & Real-World Relevance

• Food riots illustrate severe shortages when ceilings force prices far below equilibrium.
• Uber demonstrates large CS in disruptive markets; policy should weigh benefits to riders vs. losses to taxi-medallion holders.
• Minimum wage debates hinge on magnitude of DWL vs. income redistribution.
• Tax design (e.g., carbon taxes) evaluated by incidence and excess burden metrics.