Perfect Competition in Markets with Adverse Selection

Transcription

1 Perfect Competition in Markets with Adverse Selection Eduardo Azevedo and Daniel Gottlieb (Wharton) Presented at Frontiers of Economic Theory & Computer Science at the Becker Friedman Institute August 13, 2016 Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

2 Introduction Agenda Adverse selection is considered a first-order problem in many markets, which are already heavily regulated in complicated ways: Mandates, community rating, risk adjustment, differential subsidies, regulation of contract characteristics. All of these affect contract characteristics. This is a challenge to the standard models (Akerloff / Eivan Finkelstein and Cullen, and Rothschild and Stiglitz). Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

3 Introduction This paper Develops a price-taking model of adverse selection. Contract characteristics are endogenous. Consumers can be heterogeneous in more than one dimension. Equilibrium always exists. Basic idea: Start from broad set of potential contracts. Use the same logic as price-taking models (Akerlof and Einav-Finkelstein and Cullen) to determine both prices and which contracts are traded. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

4 Determining prices p D(p) p AC(q) q

5 Determining which contracts are traded

6 Preview: Unintended Consequences No Mandate Mandate (Density) Coverage

7 Model Outline 1 Model 2 Competitive Equilibrium 3 Application: Equilibrium Effects of a Mandate 4 Inefficiency and Policy Interventions Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

8 Model Model Consumers θ Θ, distributed according to a probability distribution µ. Contracts (or products) x X. Agent θ has utility U(x, p, θ) of buying x at a price p, and the cost is c(x, θ) 0 Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

9 Model Example we understand: Akerlof QJE 1970 Basic framework in Einav, Finkelstein and Cullen (2010), Hackman, Kolstad and Kowalski (2014), Handel, Hendel and Whinston (2014), Smetters and Scheuer (2014). Single, exogenous product: X = {0, 1}. Quasilinear utility, U = u(x, θ) p. Single product is often not realistic. No predictions on contract terms. In particular, the model is silent about intensive margin regulations. Yields useful predictions on pricing and efficiency. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

10 Model Equilibria All that matters are willingness to pay and costs, u(1, θ) and c(1, θ). Can define demand D(P), and average cost AC(Q) curves. Equilibria are intersection of demand and average cost. p D(p) p AC(q) Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51 q

11 Model Toy example: Rothschild and Stiglitz QJE 1976 All consumers have same wealth, same risk preferences, and may suffer a loss of the same size. Only two types, who differ in their probability of a loss, Θ = {L, H}. Contracts specify % of loss covered, X = [0, 1]. Even in this setting, equilibria do not necessarily exist. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

12 Model Interesting example: Einav, et al. AER 2013 A model of health insurance. Higher dimensional heterogeneity of consumers: Loss distributions. Risk aversion. Moral hazard parameters. Will calibrate this model to illustrate ideas, with set of contracts X = [0, 1] being % of coverage. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

13 Model Interesting example: Einav, et al. AER 2013 A model of health insurance. Higher dimensional heterogeneity of consumers: Loss distributions. Risk aversion. Moral hazard parameters. Will calibrate this model to illustrate ideas, with set of contracts X = [0, 1] being % of coverage. Assuming CARA preferences, u(x, θ) = x M θ + x 2 2 H θ x(2 x) S2 θ A θ, and c(x, θ) = x M θ + x 2 H θ. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

14 Model Assumptions Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

15 Model Assumptions Simpler assumptions for the talk: 1 X and Θ are compact subsets of Euclidean space. 2 U(x, p, θ) = u(x, θ) p, where u is Lipschitz in x. 3 u and c are continuous. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

16 Model Prices and allocations A price is a measurable function p over X, price of contract x denoted p(x). An allocation α is a measure over Θ X such that α Θ = µ. Given (p, α), consumers are optimizing if, for (x, θ) with probability 1 according to α, for all x X, u(x, θ) p(x) u(x, θ) p(x ). Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

17 Model Prices and allocations A price is a measurable function p over X, price of contract x denoted p(x). An allocation α is a measure over Θ X such that α Θ = µ. Given (p, α), consumers are optimizing if, for (x, θ) with probability 1 according to α, for all x X, u(x, θ) p(x) u(x, θ) p(x ). Conditional moments are denoted as E x [c] = E[c( x, θ) α, x = x]. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

18 Equilibrium Outline 1 Model 2 Competitive Equilibrium 3 Application: Equilibrium Effects of a Mandate 4 Inefficiency and Policy Interventions Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

19 Equilibrium Weak equilibrium Definition A price-allocation pair (p, α) is weak equilibrium if 1 Consumers optimize. 2 All contracts make 0 profits, p(x) = E x [c] almost everywhere according to α. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

20 Equilibrium Weak Equilibrium Example: Rothschild-Stiglitz X = [0, 1] and Θ = {L, H}. H p(x) L IC H IC L x 0 1 Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

21 Equilibrium But there are many other weak equilibria X = [0, 1] and Θ = {L, H}. H p(x) IC H L IC L p(x) 0 1 Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51 x

22 Equilibrium Definition: Perturbations A behavioral type x is an agent who always demands contract x, u(x, x) =, u(x, x) = 0 if x x, and c(x, x) = 0. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

23 Equilibrium Definition: Perturbations A behavioral type x is an agent who always demands contract x, u(x, x) =, u(x, x) = 0 if x x, and c(x, x) = 0. A perturbation ( X, η) is an economy with a finite set of contracts X X, set of types and distribution of types Θ X, µ + η, where the support of η is X. We can define unrefined equilibria of perturbations because every perturbation is a particular case of the model. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

24 Equilibrium of a Perturbation: Example L IC H IC L H x

25 Equilibrium of a Perturbation: Example $8,000 $6,000 Equilibrium Prices Average Loss Parameter ($) $4,000 $2,000 $ Contract

26 Equilibrium Definition: Perturbations (continued) A sequence of perturbations ( X n, η n ) n N converges to the original economy if 1 Every point in X is the limit of a sequence (x n ) n N with each x n X n. 2 The mass of behavioral types η n ( X n ) converges to 0. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

27 Equilibrium Definition: Perturbations (continued) Consider a sequence of perturbations ( X n, η n ) n N converging to the original economy. A sequence of weak equilibria (p n, α n ) n N converges to (p, α ) if 1 The allocations α n ((Θ X) X) converge to α weakly. 2 For every sequence (x n ) n N, with each x n X n and limit x X, we have that p n (x n ) converges to p (x). Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

28 Equilibrium Equilibrium Definition (p, α ) is a competitive equilibrium if there exists a sequence of perturbations converging to the original economy with a sequence of weak equilibria that converges to (p, α ). Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

29 Equilibrium: Example L IC H IC L H x

30 Equilibrium: Example L IC H IC L H x

31 Equilibrium: Example p(x) L IC H IC L H x

32 Equilibrium Existence Theorem A competitive equilibrium exists. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

33 Equilibrium Proof Outline Step 1: Every perturbed economy has an equilibrium, by a standard fixed point argument. Step 2: Equilibrium prices in every perturbed economy are uniformly Lipschitz. Step 3: Every sequence of perturbations converging to the original economy has a convergent subsequence, and the limit is an equilibrium of the original economy. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

34 Equilibrium Equilibrium properties Proposition 1 Every equilibrium is a weak equilibrium. 2 Equilibrium prices are continuous and almost everywhere differentiable. 3 For every contract x with strictly positive equilibrium price there exists a consumer θ who is indifferent between her current contract and x. Moreover, c(x, θ) p(x). Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

35 Equilibrium Strategic Foundations The paper shows that the competitive model is a particular limiting case of Bertrand competition with differentiated products. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

36 Equilibrium Strategic Foundations The paper shows that the competitive model is a particular limiting case of Bertrand competition with differentiated products. In particular, this means that competitive models (Rothschild and Stiglitz, Akerlof, Riley) are limiting cases of the differentiated-products models used in empirical IO (Starc, Veiga and Weyl). Key assumptions: Many, small firms, with a small degree of differentiation. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

37 Equilibrium Bertrand Game (definitions) Fix a perturbation (E, X, η). n firms selling differentiated varieties of each product x. Logit shares S(P, p, x, θ) equal to e σ (u(x,θ) P) e σ (u(x,θ) P) + (n 1) e σ (u(x,θ) p(x)) + x x n eσ (u(x,θ) p(x )). Profits Π(P, p, x) = S(P, p, x, θ) (P c(x, θ)) d(µ + η) θ if firms produce less than scale q or if the firm produces more. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

38 Equilibrium Bertrand Game (result) Proposition There exists a constant K such that, if 1 < q < K, n then an equilibrium exists. Moreover, profits per unit sold are lower than 2 σ. Can show that with fixed small scale and large number of firms, as elasticities go to infinity equilibria converge to the perfectly competitive outcome. Bottom line: perfect competition is the limit of a Bertrand game with many, small, and undifferentiated firms. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

39 Equilibrium Literature Other GE notions: Gale Restuds (1992), Dubey and Geanakoplos QJE (2002). In one-dimensional case, coincides with some standard notions from the signaling and screening literatures: Rothschild and Stiglitz, when their equilibrium exists. Riley Ecma (1979) reactive equilibrium. Banks and Sobel Ecma (1987) D1. Bisin and Gottardi JPE (2006) EPT equilibrium. But differs from notions that allow firms to cross-subsidize contracts: Wilson JET (1977) - Miyazaki BJE (1977) anticipatory equilibrium. Netzer and Scheuer IER (2014). Veiga and Weyl (2014) Complementary to our work, many similar comparative statics. Key differences are imperfect competition and product variety (tomato sauce). Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

40 Calibration Outline 1 Model 2 Competitive Equilibrium 3 Application: Equilibrium Effects of a Mandate 4 Inefficiency and Policy Interventions Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

41 Calibration Calibration: Einav et al. health insurance model u(x, θ) = x M θ + x 2 2 H θ x(2 x) S2 θ A θ, and c(x, θ) = x M θ + x 2 H θ. A H M S Mean 1.5E-5 1,330 4,340 24,474 Log covariance A H σlog 2 H = M S 0.25 Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

42 Equilibrium prices and adverse selection $8,000 $6,000 Equilibrium Prices Average Loss Parameter ($) $4,000 $2,000 $ Contract

43 Equilibrium demand profile Risk Aversion, A θ $1,000 $10,000 $100,000 Average Loss, M θ

44 Simulating a Mandate $8,000 $6,000 No Mandate Prices No Mandate Losses Mandate Prices Mandate Losses ($) $4,000 $2,000 $ Contract

45 Unintended Consequences No Mandate Mandate (Density) Coverage

46 Calibration Theoretical Results Consider an economy with mandated coverage [m + dm, 1], and equilibria (p dm, α dm ). We will derive comparative statics with respect to dm. Denote (p 0, α 0 ) as (p, α). See the paper for necessary regularity conditions. Define the intensive margin selection coefficient as S I (x) = x E x [c] E x [mc]. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

47 Calibration Theoretical Results Proposition The change in the prices of minimum coverage is lim dmp dm (x) dm=0 = S I (m) + ξ, x m where the error term ξ is small if g(m)/g(m) is small. Proposition Whenever S I (m) 0, there are consumers who change their decisions beyond the direct effects of the mandate. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

48 Optimal Regulation Outline 1 Model 2 Competitive Equilibrium 3 Application: Equilibrium Effects of a Mandate 4 Inefficiency and Policy Interventions Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

49 Informal Example Will cover main ideas behind optimal regulation in a simple informal example. Let X = [0, 1]. Assume that consumers only adjust in the intensive margin when prices change. A benevolent government can regulate menus and prices, but has the same information as the firms. Kaldor-Hicks efficiency, no excess burden of public funds.

50 Optimal Regulation Equilibrium Inefficiency Starting point for regulation: equilibria are inefficient. Definitions: Marginal cost mc(x, θ) = x c(x, θ). Marginal utility mu(x, θ) = x u(x, θ). Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

51 Equilibrium is Inefficient Private optimum where marginal utility equals p. p mu θ x eq x

52 Equilibrium is Inefficient But social optimum where marginal utility equals marginal cost. p mc θ x eq x eff mu θ x

53 Equilibrium is Inefficient Two distortions: E x[mc] p and mc θ E x[mc]. p E x [mc] mc θ x eq x eff mu θ x

54 Equilibrium is Inefficient Sources: adverse / advantageous selection and multidimensional heterogeneity. p S I E x [mc] mc θ x eq x eff mu θ x

55 Optimal Regulation Optimal Regulation Effectively, any regulation can be implemented setting p(x). It is insightful to write a formula for the per unit subsidy the government must give firms, p(x) + t(x) = E x [c]. Will now find necessary conditions for optimum by perturbing a price schedule. This is an old trick in optimal tax theory that has seen a revival since the 2000s. Increase p by dp in the interval x + dx. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

56 Perturbation p(x) 0 x x x+dx 1

57 Perturbation p(x) p(x) 0 x x x+dx 1

58 Optimal Regulation Perturbation (continued) Denote intensive margin elasticity as ɛ(x, θ). In an optimal price schedule, it must be that E x [ɛ (mu mc)] = 0. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

59 Optimal Regulation Perturbation (continued) Denote intensive margin elasticity as ɛ(x, θ). In an optimal price schedule, it must be that E x [ɛ (mu mc)] = 0. We have 0 = E x [p mc] E x [ɛ] + Cov x [ mc, ɛ] = (S I t ) E x [ɛ] Cov x [mc, ɛ]. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

60 Optimal Regulation Consequences Optimal regulation is a modified risk adjustment formula: risk adjustment plus covariance term: t (x) = S I (x) Cov x[ɛ, mc] E x [ɛ] Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

61 Regulation Example $8,000 $6,000 No Mandate Prices No Mandate Losses Mandate Prices Mandate Losses ($) $4,000 $2,000 $ Contract

62 Regulation Example $8,000 $6,000 Equilibrium Prices Equilibrium Losses Optimum Prices Optimum Losses ($) $4,000 $2,000 $ Contract

63 Optimal Regulation Consequences The mandate raises welfare by $127 per consumer. Optimal regulation increases it by $279. A simple policy like the mandate can increase efficiency. But also has important unintended consequences: with adverse selection mandates subsidize low-quality coverage. Optimal policy also addresses selection in the intensive margin. Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51

64 Optimal Regulation Conclusion Key idea is to apply the supply and demand approach from the one-contract model to a more general case. Gives a simple model to explain what contracts are traded, and effects of policy. Standard policies have important unintended consequences, and regulation should also address selection on the intensive margin. Thank You! Eduardo Azevedo (Wharton) Adverse Selection August 13, / 51