Liquidity, Asset Price, and Welfare

Transcription

1 Liquidity, Asset Price, and Welfare Jiang Wang MIT October 20, 2006 Microstructure of Foreign Exchange and Equity Markets Workshop Norges Bank and Bank of Canada

2 Introduction Determinants of liquidity? Need for liquidity (non-synchronization in trading). Supply of liquidity. Importance of liquidity? Asset prices. Market stability. Welfare. Wang Liquidity, Asset Price, and Welfare 1

3 Intuition 1. Two elements essential to liquidity: need to trade and cost to trade. 2. Costs affect liquidity provision and prices, taken liquidity needs as given. 3. But the same costs give rise to liquidity needs in the first place. 4. Without participation costs, there is no need for liquidity. Trading needs come from idiosyncratic shocks, which sum to zero. Trades are synchronized and do not move prices. The market is perfectly liquid (only fundamentals move prices). 5. With participation costs, there is need for liquidity. Not all traders are present in the market. Traders with offsetting trading needs have different trading gains. Trades are non-synchronized, which leads to need for liquidity. Wang Liquidity, Asset Price, and Welfare 2

4 Setup (1) 1. Assets: A riskless bond and a risky stock. Bond pays constant (positive) interest rate r. Stock pays dividend D t+1, with mean D and volatility σ D. 2. Agents: Homogenous preference, information, but heterogenous risks. Same initial asset holdings: θ shares of stock. Different non-traded payoff N i t+1 for agent i: N i t+1 =(Y t+λ i X t ) n t+1, λ i =1or 1 with equal probabilities. Y t gives aggregate non-traded risk. Idiosyncratic risks λ i X t sum to zero: Nt+1 i = Y t n t+1. i Denote agents with λ i X t > 0 and < 0 as a and b, respectively. Wang Liquidity, Asset Price, and Welfare 3

5 Setup (2) 3. Costs of Participation: Cost to be a market maker c m (paid ex ante). Cost for spot participation c (paid before trading). 4. Simplifications for tractability and easy exposition: Constant absolute risk aversion α. Normal shocks (Y t,x t,d t+1,n t+1, t =0, 1,...). Stock and non-traded payoffs correlated. Y t =0for simplicity. Wang Liquidity, Asset Price, and Welfare 4

6 Definition of Equilibrium 1. Agents optimize over Participation decisions: ηm i =0, 1 and ηi t =0, 1. Be a market maker (η m =1) and trade at all times Be a trader and pay a cost to trade (η =1) when needed. Trading decisions: Stock holding θt i(ηi m,ηi t 1 ). Shocks X t X t+1 t t+1 time Choices η m ηt i θt+1 i (η m,ηt i) 2. Participation reaches equilibrium. A fraction μ of agents become market makers. Among traders, fraction ωt i enter the market, i = a, b. 3. Stock market clears among participating agents. Wang Liquidity, Asset Price, and Welfare 5

7 Zero Participation Costs All agents are in the market at all times, μ =1and/or ω a t = ωb t =1. The equilibrium price and agents stock holdings are: P t = D r ασ2 D θ θ i t = θ λ i X t Agents with λ i X t >0 are sellers (a) and λ i X t <0 are buyers (b). Trading needs are perfectly matched (λ a X t = λ b X t ). Trades are synchronized and there is no need for liquidity. Prices depend only on fundamentals ( D and θ), independent of individual trading needs (X t ). Wang Liquidity, Asset Price, and Welfare 6

8 Optimal Trading Policy Under Costly Participation Trading becomes infrequent. A trader s net risk exposure is θ t + λ i X t z t z t Time (in years) Desirable exposure z. (Without cost, z = θ.) Trade occurs only when net risk exposure exceeds certain limits. Upper and lower limit, z + δ a and z δ b, respectively. In general, δ a δ b. Wang Liquidity, Asset Price, and Welfare 7

9 Asymmetric Trading Gains Let v(θ) E[u(θ, )] and θ be the optimal holding, i.e., v (θ )=0. v v Θ x Θ Θ x Θ For small deviations from optimum, trading gains are symmetric: v(θ ) v(θ +x) 1 2 v (θ )(x) 2 = 1 2 v (θ )( x) 2 v(θ ) v(θ x). With costs, traders trade only when they are far away from the optimum. Trading gains differ between traders with offsetting trading needs. Wang Liquidity, Asset Price, and Welfare 8

10 Sellers Expect Larger Trading Gains Than Buyers With trading needs only are partially met, risk sharing is not perfect. Having to bear idiosyncratic risks, traders become more risk averse. True for standard risk aversion (DARA and DAP) (Kimball, 1993). Traders stock demand decreases after new idiosyncratic shocks. Sellers become further away from desired holdings than buyers. Sellers enter market before buyers! Wang Liquidity, Asset Price, and Welfare 9

11 Non-synchronized Trading and Order Imbalances In equilibrium, sellers participate more than buyers: ωt a ωb t. Order imbalance is usually negative: Δ t (1 μ)(ωa t ωb t )λa X t+1, E[Δ t+1 X t ] 0. Liquidity needs, when arise, are sell orders of large sizes. (a) Equilibrium Participation Rate ω a,ω b Trader Participation Rate 1 (b) Order Imbalance Order Imbalance X 0.5 seller buyer -0.1 X Parameter values: σ D =0.25, θ =1, σ X =0.6, σ nd =0.0625, α =4, c =0.1, μ = 1 3. Wang Liquidity, Asset Price, and Welfare 10

12 The equilibrium stock price is P t = D r ασ2 D θ d + p t Stock Price Fundamental value D/r ασ 2 D θ P. Illiquidity discount d. Impact of order imbalance (liquidity need) p t. p t consists of two components: p t = p t + u t : p t depends on expected future order imbalance E[Δ t+1 X t ] 0 u t depends on unexpected current order imbalance. Liquidity need, when arises, influences stock price negatively, p 0. Wang Liquidity, Asset Price, and Welfare 11

13 Liquidity and Asset Prices Calibrating the Impact of Illiquidity on Stock Prices α σ X c/ P (%) Cost as % of Average Trade Amount c/ P (%) Annual Turnover (%) c/ P (%) Illiquidity Discount (% of P ) c/ P (%) Return Premium (%) (Parameters: D =0.050, r =0.037, P =0.784, σ nd =0.0625, ασ Y =1.347, σ X =8σ Y.) Wang Liquidity, Asset Price, and Welfare 12

14 Liquidity Crashes (a) Distribution of p t Prob. Distr (b) Unconditional distribution of p t Prob. Distr E p X p Parameters values: σ D =0.25, θ =1, σ nd =0.0625, σ X =0.5, σ Y =0, α =4, c =0.1, μ = 1 3. The liquidity impact on prices has the following properties: Usually negative Large (of finite sizes), when occurs Leading to fat-tails and negative skewness in returns. Wang Liquidity, Asset Price, and Welfare 13

15 Welfare Trading enhances liquidity and generates positive externality. Market mechanism may fail to achieve efficient liquidity provision. Use Certainty Equivalence (CE) as a welfare measure. 1. Decreasing cost of spot participation can decrease welfare. Welfare and Cost of Spot Participation c c 0.04 Parameters values: σ D =0.25, θ =0, σ nd =0.0625, σ X = σ Y =0.6, α =4, cm =0.15. Wang Liquidity, Asset Price, and Welfare 14

16 2. Liquidity provision by market can be suboptimal. Welfare Gain Under Forced Participation G = CE FP CE. 0.2 G 0.1 c 0.15 c c m -0.1 c Parameters values: σ D =0.25, θ =0, σ nd =0.0625, σ X = σ Y =0.6, α =4. Wang Liquidity, Asset Price, and Welfare 15

17 Conclusion Market frictions lead to endogenous liquidity needs. Liquidity affects prices. Liquidity crashes without fundamental shocks. Fat-tails and skewness in returns. Trading generates positive externality. Market forces may fail to lead to efficient liquidity provision. Origins of participation costs? Magnitudes? Policy implications? Wang Liquidity, Asset Price, and Welfare 16