Dynamic Trading with Predictable Returns and Transaction Costs. Dynamic Portfolio Choice with Frictions. Nicolae Gârleanu

Transcription

1 Dynamic Trading with Predictable Returns and Transaction Costs Dynamic Portfolio Choice with Frictions Nicolae Gârleanu UC Berkeley, CEPR, and NBER Lasse H. Pedersen New York University, Copenhagen Business School, AQR Capital Management, CEPR, and NBER

2 Motivation: Dynamic Trading Active investors e.g., hedge funds, mutual funds, proprietary traders, individuals, other asset managers try to predict returns minimize transactions costs minimize risk Dynamic problem: investor trades now and in the future Key research questions: What is the optimal trading strategy? Does it work empirically?

3 Motivating Example An investor makes the following predictions: Based on strong fundamentals (low M/B, P/E, low accruals, high and stable earnings, etc.) the annualized expected excess return (alpha) on Centurytel Inc. is 10%. this alpha is expected to last for 2 years Based on recent catalysts, improving fundamentals and pricing, the annualized alpha of Treehouse Foods Inc. is also 10% this alpha is expected to last for half a year Based on recent demand pressure from funds with outflow, the annualized alpha of HJ Heinz Co. is -12% this alpha is expected to last for 2 weeks These and other signals are collected for numerous securities All these stocks are positively correlated The investor has estimated the trading cost (incl. market impact) for these stocks based on past experience The investor makes a similar analysis every day

4 Results: Aim in Front of the Target Closed-form optimal dynamic trading strategy

5 Results: Aim in Front of the Target Closed-form optimal dynamic trading strategy Two portfolio principles: 1. Aim in front of the target 2. Trade partially towards the current aim

6 Results: Aim in Front of the Target Closed-form optimal dynamic trading strategy Two portfolio principles: 1. Aim in front of the target 2. Trade partially towards the current aim Aim portfolio : Weighted average of current and future expected Markowitz portfolios Predictors with slower mean reversion: more weight Application topanel commodity A: Construction futures: of superior Current net Optimal returns Trade Markowitz t Position in asset 2 old position x t 1 new position x t E t (aim t+1 ) aim t Position in asset 1

7 Results: Aim in Front of the Target Closed-form optimal dynamic trading strategy Two portfolio principles: 1. Aim in front of the target 2. Trade partially towards the current aim Aim portfolio : Weighted average of current and future expected Markowitz portfolios Predictors with slower mean reversion: more weight Application topanel commodity A: Construction futures: of superior Current net Optimal returns Trade Markowitz t Position in asset 2 old position x t 1 new position x t E t (aim t+1 ) aim t Position in asset 1

8 Figure 1. Aim in front of the target. Panels A C show the optimal portfolio choice with two securities. The Markowitz portfolio is the current optimal portfolio in the absence of transaction costs: the target for an investor. It is a moving target, and the solid curve shows how it is expected to mean-revert over time (toward the origin, which could be the market portfolio). Panel A shows Aim in Front ofdynamic the Trading Target: with Predictable Finance Returns and Transaction Beyond Costs 2311 Panel A. Constructing the current optimal portfolio Panel D. Skate to where the puck is going to be Markowitz t Position in asset 2 old position x t 1 new position aim t x t E t (aim t+1 ) Position in asset 1 Panel B. Expected optimal portfolio next period Panel E. Shooting: lead the duck Position in asset 2 x t 1 x t Et (x t+1 ) E t (Markowitz t+1 ) Position in asset 1 Panel C. Expected future path of optimal portfolio Panel F. Missile systems: lead homing guidance Position in asset 2 E t (x t+h ) E t (Markowitz t+h ) Position in asset 1

9 Related Literature Optimal trading with transactions costs, no predictability Constantinides (86), Amihud and Mendelson (86), Vayanos (98), Liu (04) Predictability, no transactions costs Merton (73), Campbell and Viceira (02) Optimal trade execution with exogenous trade: Perold (88), Almgren and Chriss (00) Numerical results with time-varying investment opportunity set Jang, Koo, Liu, and Loewenstein (07), Lynch and Tan (08) Quadratic programming Used in macroeconomics (Ljungqvist and Sargent (04)) and other fields: solve up to Ricatti equations Grinold (06)

10 Outline of Talk Basic model Optimal portfolio strategy: Aim in front of the target Persistent price impact Application: Commodity futures

11 Discrete-Time Model Returns: r s t+1 = k Risk: var t (u t+1 ) = Σ β sk f k t }{{} =E t(r s t+1 ) +u s t+1 Alpha decay: f k t+1 = j Φkj f j t + ε t+1 Transaction costs:whatever TC( x t ) = 1 2 x t Λ x t Assumption A:whatever Λ = λσ Objective: max xt E t (1 ρ)t+1 ( x t r t+1 γ 2 x t Σx t ) (1 ρ) t 2 x t Λ x t

12 Solution Method: Dynamic Programming Introduce value function V that solves the Bellman equation: { V (x t 1, f t) = max 1 ( x t 2 x t Λ x t + (1 ρ) xt E t(r t+1 ) γ ) } 2 x t Σx t + E t[v (x t, f t+1 )] Proposition The model has a unique solution and the value function is given by V (x t, f t+1 ) = 1 2 x t A xx x t + x t A xf f t f t+1a ff f t+1 + A 0. The coefficient matrices A xx, A xf, A ff can be solved explicitly and A xx is positive definite.

13 Trade Partially Towards the Aim Proposition (Trade Partially Towards the Aim) i)the optimal dynamic portfolio x t is: x t = x t 1 + Λ 1 A xx (aim t x t 1 ) with trading rate Λ 1 A xx and aim t = A 1 xx A xf f t

14 Trade Partially Towards the Aim Proposition (Trade Partially Towards the Aim) i)the optimal dynamic portfolio x t is: x t = x t 1 + Λ 1 A xx (aim t x t 1 ) with trading rate Λ 1 A xx and aim t = A 1 xx A xf f t ii) Under Assumption A, the trading rate is the scalar a/λ = (γ + λρ) + (γ + λρ) 2 + 4γλ(1 ρ) 2(1 ρ)λ < 1 The trading rate is decreasing in transaction costs λ and increasing in risk aversion γ.

15 What is the Target and What is the Aim? What is the moving target, i.e., the optimal position in the absence of transaction costs? Markowitz t = (γσ) 1 Bf t What is the aim portfolio?

16 Aim in Front of the Target Proposition (Aim in Front of the Target) (i) The aim portfolio is the weighted average of the current Markowitz portfolio and the expected future aim portfolio. Under Assumption A, letting z = γ/(γ + a): aim t = z Markowitz t + (1 z) E t (aim t+1 ). (ii) The aim portfolio is the weighted average of the current and future expected Markowitz portfolios. Under Assumption A, aim t = z(1 z) τ t E t (Markowitz τ ) τ=t The weight of the current Markowitz portfolio z decreases with transaction costs λ and increases in risk aversion γ.

17 Aim in Front of the Target: Illustration Panel A: Construction of Current Optimal Trade Markowitz t Position in asset 2 old position x t 1 new position x t target t E t (target t+1 ) Position in asset 1

18 Aim in Front of the Target: Illustration Panel B: Expected Next Optimal Trade Position in asset 2 x t 1 x t E t (x t+1 ) E t (Markowitz t+1 ) Position in asset 1

19 Aim in Front of the Target: Illustration Panel C: Expected Evolution of Portfolio Position in asset 2 E t (x t+h ) E t (Markowitz t+h ) Position in asset 1

20 Weight Signals Based on Alpha Decay Proposition (Weight Signals Based on Alpha Decay) (i) Under Assumption A, the aim portfolio is: ( aim t = (γσ) 1 B I + a ) 1 γ Φ f t (ii) If the matrix Φ is diagonal, Φ = diag(φ 1,..., φ K ), then the aim portfolio is: ( aim t = (γσ) 1 B f 1 t 1 + φ 1 a/γ,..., ft K 1 + φ K a/γ I.e., the aim pf. is the Markowitz pf. with factors f k t scaled down based on their own alpha decay given by Φ. )

21 Weight Signals Based on Alpha Decay: Illustration Panel A: Construction of Current Optimal Trade Markowitz t Position in asset 2 old position x t 1 new position x t E t (aim t+1 ) aim t Position in asset 1

22 Position Homing In Proposition (Position Homing In) Suppose that the agent has followed the optimal trading strategy from time until time t. Then the current portfolio is an exponentially weighted average of past aim portfolios. Under Assumption A, x t = t τ= a λ (1 a λ )t τ aim τ (1)

23 Example: Timing a Single Security A security has risk Σ = σ 2 and return The optimal strategy is r t+1 = k β k f k t }{{} =E t(r t+1 ) +u t+1 x t = ( 1 a ) x t 1 + a λ λ 1 γσ 2 K i=1 β i 1 + φ i a/γ f i t.

24 Example: Relative-Value Trades w/ Security Characteristics Each security s (e.g., IBM) has its own characteristics ft i,s (e.g., its value and momentum) and characteristics predict returns for all securities, with the same coefficients: E t (r s t+1) = i β i f i,s t Each characteristic has the same mean-reversion speed for all securities f i,s t+1 = φi ft i,s + ε i,s t+1.

25 Example: Relative-Value Trades w/ Security Characteristics Each security s (e.g., IBM) has its own characteristics ft i,s (e.g., its value and momentum) and characteristics predict returns for all securities, with the same coefficients: E t (r s t+1) = i β i f i,s t Each characteristic has the same mean-reversion speed for all securities f i,s t+1 = φi ft i,s + ε i,s t+1. The optimal characteristic-based strategy is x t = ( 1 a ) x t 1 + a I β i λ λ (γσ) φ i a/γ f t i. i=1

26 Example: Static Model When the future is completely discounted (ρ = 1), objective is max (x t E t (r t+1 ) γ2 x t Σx t λ2 ) x t Σ x t x t

27 Example: Static Model When the future is completely discounted (ρ = 1), objective is max (x t E t (r t+1 ) γ2 x t Σx t λ2 ) x t Σ x t x t Solution x t = λ γ + λ x t 1 + γ γ + λ (γσ) 1 E t (r t+1 ). No choice of γ, λ recovers the dynamic solution.

28 Example: Signals (Equally) Valuable for K Days Suppose: All factors equally good B = (β,..., β) Today s yesterday is tomorrow s day-before-yesterday: ft+1 1 = ε 1 t+1 ft+1 k = ft k 1 for k > 1

29 Example: Signals (Equally) Valuable for K Days Suppose: All factors equally good B = (β,..., β) Today s yesterday is tomorrow s day-before-yesterday: Optimal strategy: x t = ft+1 1 = ε 1 t+1 ft+1 k = ft k 1 for k > 1 ( 1 a ) x t 1 + a λ λ where z = a/(a + γ) < 1. β σ 2 (1 z) k ( 1 z K+1 k) f k t, More weight to recent signals even if they don t predict better.

30 Persistent Transaction Costs Model Proposition With temporary and persistent transaction costs, the optimal portfolio x t is x t = x t 1 + M rate (aim t x t 1 ), which tracks an aim portfolio, aim t = M aim y t, that depends on the return-predicting factors and the price distortion.

31 Persistent Transaction Costs Model Panel A: Only Transitory Cost Position in asset 2 E t (x t+h ) E t (Markowitz t+h ) Position in asset 1 Panel B: Persistent and Transitory Cost Position in asset 2 E t (x t+h ) E t (Markowitz t+h ) Position in asset 1 Panel C: Only Persistent Cost Position in asset 2 E t (x t+h ) E t (Markowitz t+h ) Position in asset 1

32 Application: Dynamic Trading of Commodity Futures Data on liquid futures without tight price limits 01/01/ /23/2009: Aluminum, Copper, Nickel, Zinc, Lead, Tin from London Metal Exchange (LME) Gas Oil from the Intercontinental Exchange (ICE) WTI Crude, RBOB Unleaded Gasoline, Natural Gas from New York Mercantile Exchange (NYMEX) Gold, Silver is from New York Commodities Exchange (COMEX) Coffee, Cocoa, Sugar from New York Board of Trade (NYBOT)

33 Predicting Returns and Other Parameter Estimates Pooled panel regression: rrrt+1 s = f 5D,s t ft ft + ut+1 s (0.17) (2.22) (2.82) ( 1.79) Alpha decay: f 5D,s 1Y,s t+1 = ft 5D,s + ε 5D,s 1Y,s 1Y,s ft+1 = ft + ε 5Y,s 5Y,s ft+1 = ft + ε t+1 1Y,s t+1 5Y,s t+1 Risk: Σ estimated using daily price changes Absolute risk aversion: γ = 10 9 Time discount rate: ρ = 1 exp( 0.02/260) Transactions costs: λ = , as well as λ high = Y,s

34 Performance of Trading Strategies Before and After TCs Panel A: Benchmark Transaction Costs Panel B: High Transaction Costs Gross SR Net SR Gross SR Net SR Markowitz Dynamic optimization Static optimization Weight on Markowitz = 10% Weight on Markowitz = 9% Weight on Markowitz = 8% Weight on Markowitz = 7% Weight on Markowitz = 6% Weight on Markowitz = 5% Weight on Markowitz = 4% Weight on Markowitz = 3% Weight on Markowitz = 2% Weight on Markowitz = 1%

35 Positions in Crude and Gold Futures 6 x Position in Crude 104 Markowitz Optimal x Position in Gold 105 Markowitz Optimal /02/98 05/29/01 02/23/04 11/19/ /02/98 05/29/01 02/23/04 11/19/06

36 Optimal Trading in Response to Shock to 5-Day Return-Predicting Signal 3.5 x 104 Optimal Trading After Shock to Signal 1 (5 Day Returns) 3 Markowitz Optimal Optimal (high TC)

37 Optimal Trading in Response to Shock to 1-Year Return-Predicting Signal x 105 Optimal Trading After Shock to Signal 2 (1 Year Returns) 3 Markowitz Optimal Optimal (high TC)

38 Optimal Trading in Response to Shock to 5-Year Return-Predicting Signal 1 0 x 105 Optimal Trading After Shock to Signal 3 (5 Year Returns) Markowitz Optimal Optimal (high TC)

39 New paper: Dynamic Portfolio Choice with Frictions What s different in this paper: Continuous time Micro foundation for transaction costs Connection between discrete and continuous time What happens when trading becomes more frequent? Generalized factor dynamics and return dynamics, including stochastic volatility Equilibrium implications

40 Conclusion: Aim in Front of the Target Derive the closed-form optimal dynamic portfolio strategy 1. Aim in front of the target 2. Trade partially towards the current aim at constant rate 3. Give more weight to persistent factors Superior net returns in application