Public economics Study Guide

📖 Core Concepts Public Economics – Study of government policy using efficiency (maximizing total welfare) and equity (fair distribution). Market Failure – Situations where private markets do not allocate resources efficiently or equitably. Public Goods – Non‑rival (one’s use doesn’t reduce another’s) and non‑excludable (no one can be barred). Pure examples: national defense, knowledge. Most are impure (some rivalry or excludability). Externalities – Abyssal effects of one agent’s production/consumption on others. Positive: education, public health. Negative: pollution, noise, non‑vaccination. Imperfect Competition – Differentiated products, barriers to entry, pricing/quantity away from the competitive optimum → social cost above the efficient level. Tax Incidence – Who actually bears the economic burden of a tax (different from who the law says pays it). Optimal Taxation – Design tax structures that balance efficiency and equity. Diamond–Mirrlees Theorem – Even without lump‑sum taxes, production efficiency remains desirable; integrates distributional concerns with revenue‑raising. Pigouvian Tax – Tax that sets price = marginal social cost (MSC) to internalize a negative externality. Coase Theorem – With well‑defined property rights and low transaction costs, parties can bargain to the efficient outcome without taxes. Preference Aggregation – Revealing individual desired levels of public goods (via voting, lobbying, etc.). Social Choice Theory – How groups make collective decisions; constitutional “rules of the game’’ constrain majorities and protect minorities. --- 📌 Must Remember Public good = non‑rival + non‑excludable. Pigouvian tax corrects the gap MSC – MPC. Coase theorem works only when transaction costs are negligible. Diamond–Mirrlees: keep production efficient even if taxes aren’t lump‑sum. Tax price = extra dollars an individual pays for a $1 increase in government spending. Higher‑income → higher tax price → preference for less public‑good provision. Market failure → government intervention (taxes, provision, regulation). Imperfect competition → social cost > competitive cost → regulation/antitrust. --- 🔄 Key Processes Identify Market Failure Check for non‑rivalry, non‑excludability, externalities, or imperfect competition. Choose Policy Tool Externality: Pigouvian tax or Coase bargaining (if low transaction costs). Public Good under‑production: Government provision or subsidies. Imperfect competition: Antitrust/price regulation. Design Pigouvian Tax Compute marginal private cost (MPC) and marginal social cost (MSC). Set tax $t = MSC - MPC$ so that private marginal cost = MSC. Cost–Benefit Analysis (CBA) Estimate ΔBenefit and ΔCost for a policy. Compute Net Present Value (NPV) = Σ (Benefitt – Costt)/(1+r)^t. Accept if NPV > 0. Aggregate Preferences Collect individual willingness‑to‑pay (WTP) for public goods. Use voting or revealed‑preference mechanisms, aware of lobbying distortions. --- 🔍 Key Comparisons Public vs Private Good Public: non‑rival, non‑excludable. Private: rival, excludable. Pigouvian Tax vs Coase Solution Pigouvian: tax = MSC‑MPC, works regardless of bargaining power. Coase: relies on private bargaining, zero transaction costs, well‑defined rights. Pure vs Impure Public Good Pure: fully non‑rival & non‑excludable (e.g., national defense). Impure: some rivalry or excludability (e.g., congested parks). Lump‑Sum Tax vs Distortionary Tax Lump‑sum: no efficiency loss, rarely feasible. Distortionary (income, sales): can cause deadweight loss, but may be needed for revenue. --- ⚠️ Common Misunderstandings “All public goods are free.” – They are non‑excludable, not costless; provision often requires taxes. “Coase theorem solves every externality.” – Fails when transaction costs are high or rights are unclear. “Pigouvian tax always eliminates deadweight loss.” – Only if tax equals the exact MSC‑MPC gap. “Tax incidence = statutory incidence.” – Economic incidence depends on relative elasticities, not who writes the check. --- 🧠 Mental Models / Intuition “Side‑effect price tag” – Think of a Pigouvian tax as putting a price on the external side‑effect so producers internalize it. “Zero‑cost bargaining” – Coase works like two kids swapping toys without any friction; any friction (transaction cost) breaks the deal. “Non‑rival = crowd‑free” – If you can add a user without reducing anyone else’s benefit, the good is non‑rival. “Diamond–Mirrlees = keep the factory running efficiently even if you can’t tax the owners directly.” --- 🚩 Exceptions & Edge Cases Impure public goods may be partially provided by markets (e.g., toll roads). High transaction costs → Coase fails; government tax/regulation needed. Government failure (political distortion, lobbying) can worsen outcomes despite good theory. Low‑income vs high‑income tax price – Wealthier groups bear a larger marginal tax burden, influencing their public‑good preferences. --- 📍 When to Use Which Negative externality + measurable MSC‑MPC → Pigouvian tax. Externality with clear property rights & low bargaining costs → Coase bargaining. Pure public good under‑provided → Government provision or subsidy. Imperfect competition → Antitrust or price regulation. Policy evaluation → Cost‑Benefit Analysis (especially for large projects). Distributional concerns → Diamond–Mirrlees framework to keep production efficient while adjusting tax structures. --- 👀 Patterns to Recognize Question mentions “non‑rival & non‑excludable” → Public good. “Marginal private cost < marginal social cost” → Candidate for Pigouvian tax. “Well‑defined property rights + low transaction costs” → Coase solution applicable. “Deadweight loss” + “tax” → Check if tax equals external cost; otherwise, it’s a distortion. “Higher‑income group prefers less public spending” → Look for tax price argument. --- 🗂️ Exam Traps Distractor: “Lump‑sum taxes are always optimal.” – True for efficiency but often infeasible; other taxes may be necessary. Distractor: “All externalities can be fixed with a tax.” – Ignores cases where transaction costs are too high or benefits are hard to measure. Distractor: “Public goods are always provided by the government.” – Impure goods may be privately supplied or mixed. Distractor: “Coase theorem guarantees the socially optimal outcome regardless of who holds rights.” – Outcome depends on initial allocation of rights and bargaining power. Distractor: “Tax incidence is determined solely by the legal payer.” – Real incidence depends on relative elasticities of supply and demand. ---