Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Dynamic Oligopoly Example: Dunne et al. (2013) Generalizations and extensions References Paul Schrimpf UBC Economics 565 October 8, 2014 Dynamic Oligopoly Paul Schrimpf References Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References • Reviews: • Aguirregabiria (2012) chapters • Ackerberg, Caves, and Frazer (2006) section 3 • Aguirregabiria and Mira (2010) • Doraszelski and Pakes (2007) • My notes from 628 • Key papers: • Ericson and Pakes (1995), Aguirregabiria and Mira (2007), Bajari, Benkard, and Levin (2007) Dynamic Oligopoly Paul Schrimpf Introduction 1 Introduction Model Identification 2 Model Estimation Example: Dunne et al. (2013) Generalizations and extensions References 3 Identification 4 Estimation 5 Example: Dunne et al. (2013) 6 Generalizations and extensions Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Section 1 Introduction Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Introduction Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Section 2 Model Dynamic Oligopoly Model primitives I Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References • N players indexed by i • Discrete time index by t • Player i chooses action ait ∈ A; actions of all players at = (a1t , ..., aNt ) • State xt = (x1t , ..., xNt ) ∈ X observed by econometrician and all players at time t • Private shock εit ∈ E • Payoff of player i is Ui (at , xt , εit ) • Discount factor β Dynamic Oligopoly Assumptions I Paul Schrimpf Introduction 1 A is a finite set Model 2 Payoffs additively separable in εit , Identification Ui (at , xt , εit ) = u(at , xt ) + εit (ait ) Estimation Example: Dunne et al. (2013) 3 Generalizations and extensions xt follows a controlled Markov process F(xt+1 | References It ) = F(xt+1 |at , xt ) |{z} all information at time t 4 The observed data is generated by a single Markov Perfect equilibrium 5 β is known 6 εit i.i.d. with CDF G, which is known up to a finite dimensional parameter Dynamic Oligopoly Paul Schrimpf Assumptions II Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Each of these assumptions could be (and in some papers has been) relaxed; relaxing 6 is probably most important empirically Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Value function and equilibrium I • Strategies α : (X × E )N →AN • αi is the strategy of player i • α−i is the strategy of other players • Value function given strategies: Vαi (xt , εit ) • Integrated value function ∫ ¯ α (x) = V Vαi (xt , εit )dG(εit ) ) ∫ ( α = max vi (xt , ait ) + εit (ait ) dG(εit ) ait ∈A where vαi is the choice specific integrated value function, [ ] u(ait , α−i (xt , ε−it ), xt )+ α vi (ait , xt ) =Eε−i ¯ α (xt+1 )|ait , α−i (xt , ε−it ), xt ] +βEx [V i Dynamic Oligopoly Paul Schrimpf Introduction Value function and equilibrium II Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions • Markov perfect equilibrium: given α−i , αi maximizes vi [ αi (xt , εit ) ∈ arg max Eε−i ai u (ai ,[α−i (xt , ε−it ), xt ) + εit (ai )+ ] ¯ α (xt+1 )|ait , α−i (x, tε−it ), xt +βEx V i • Conditional choice probabilities References ( ) Pαi (ai |x) =P ai = arg max vαi (j, x) + εit (j)|x ∫ = { j∈A } 1 ai = arg max vαi (j, x) + εit (j) dG(εit ). j∈A ] Dynamic Oligopoly Value function and equilibrium III Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) • Equilibrium condition in terms of conditional choice probabilities: vPi (ait , xt ) = ) u(ait , a−i , xt )+ ¯ α (xt+1 )|ait , a−i , xt ] +βEx [V P−i (a−i |xt ) i a−i ∈AN−1 Generalizations and extensions References ( ∑ where N ∏ P−i (a−i |x) = P(aj |x). j̸=i Let ∫ Λ(a|vPi (·, xt )) = { } 1 ai = arg max vPi (j, x) + εit (j) dG(εit ). j∈A Dynamic Oligopoly Paul Schrimpf Introduction Value function and equilibrium IV Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Then the equilibrium condition is that Pi (a|x) = Λ(a|vPi (·, x)) or in vector form P = Λ(vP ) • Equilibrium existence: • If Λ : [0, 1]N|X| →[0, 1]N|X| is continuous, then by Brouwer’s fixed point theorem, there exists at least one equilibrium • Λ need not be continuous, see Gowrisankaran (1999) and Doraszelski and Satterthwaite (2010) Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Section 3 Identification Dynamic Oligopoly Identification I Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions • As in single-agent dynamic decision problems given G, β, and Eε [u(0, α−i (x, ε−i ), xt )] = 0, we can identify the expectation over other player’s actions of the payoff function, ∑ Eε [u(ai , α−i (x, ε−i ), x)] = P(a−i |x)u(ai , a−i , x) a−i References • See Bajari et al. (2009), which builds on Hotz and Miller (1993) and Magnac and Thesmar (2002) • Hotz and Miller (1993) inversion shows ∗ ∗ vαi (a, x) − vαi (0, x) = q(a, P(·|x); G) for some known function q Dynamic Oligopoly Identification II Paul Schrimpf Introduction Model Identification • Use normalization and Bellman equation to recover vαi ∗ Estimation Example: Dunne et al. (2013) Generalizations and extensions References ∗ vαi (0, x) = E[u(0, α−i (x, ε−i ), x)] + {z } | =0 ∗ + βE[max vαi (a′ , x′ ) + ε(a′ )|a, x] ′ a ∈A ∗ = βE[max vαi (a′ , x′ ) ′ a ∈A | ∗ − vαi (0, x′ ) + ε(a′ )|0, x] + {z } ≡M(x,P(·|x),G) + ∗ βE[vαi (0, x′ )|0, x] ∗ M is known; can solve this equation for vαi (0, x), then ∗ ∗ vαi (a, x) = vαi (0, x) + q(a, P(·|x); G) ∗ Dynamic Oligopoly Identification III Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References ∗ ∗ • Recover E[u(ai , α−i (x, ε−i ), x)] from vαi using Bellman equation ∗ ∗ E [u(ai , α−i (x, ε−i ), x)] =vαi (ai , x)− [ ] α∗ ′ ′ ′ − βE max v (a , x ) + ε(a )|a, x i ′ a ∈A • Need exclusion to identify u(a, x) • Without exclusion order condition fails ∑ Eε [u(ai , α−i (x, ε−i ), x)] = P(a−i |x)u(ai , a−i , x) a−i If X finite, then left side takes on|A||X| identified values, but u(a, x) has |A|N |X| possible values Dynamic Oligopoly Identification IV Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions • Assume u(a, x) = u(a, xi ) where xi is some sub-vector of x. u identified if Eε [u(ai , α−i (x, ε−i ), x)] = ∑ a−i References has a unique solution for u P(a−i |x)u(ai , a−i , xi ) Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Section 4 Estimation Dynamic Oligopoly Estimation I Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References • Can use similar methods as in single agent dynamic models • Maximum likelihood max θ∈Θ,P∈[0,1]N Tm ∑ M ∑ N ∑ ( ) log Λ aimt |vPi (·, xmt ; θ) m=1 t=1 i=1 P s.t.P = Λ(v (θ)) • Nested fixed point: substitute constraint into objective and maximixe only over θ • For each θ must solve for equilibrium – computationally challenging • Λ not a contraction • What to do when equilibrium not unique? Dynamic Oligopoly Estimation II Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References • MPEC (Su and Judd, 2012): solve constrained optimization problem ˆ • 2-step estimators: estimate P(a|x) from observed actions and then max θ∈Θ Tm ∑ M ∑ N ∑ ˆ log Λ(aimt |vPi (·, xmt ; θ)) m=1 t=1 i=1 • Can replace pseudo-likelihood with GMM (Bajari, Benkard, and Levin, 2007) or least squares (Pesendorfer and Schmidt-Dengler, 2008) objective • Unlike single agent case, efficient 2-step estimators do not have same asymptotic distribution as MLE1 Dynamic Oligopoly Estimation III Paul Schrimpf Introduction Model Identification Estimation • Nested pseudo likelihood (Aguirregabiria and Mira, 2007): after 2-step estimator update (k−1) ˆ (k−1) )), re-maximize pseudo likelihood to ˆ(k) = Λ(vPˆ (θ P (k) ˆ get θ Example: Dunne et al. (2013) Generalizations and extensions • Asymptotic distribution depends on number of References iterations; if iterate to convergence, then equal to MLE 1 In single agent models efficient 2-step and ML estimators have the same asymptotic distribution but different finite sample properties. Dynamic Oligopoly Paul Schrimpf Incorporating static parameters Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References • Often some portion of payoffs can be estimated without estimating the full dynamic model • E.g. Holmes (2011) estimates demand and revenue from sales data, costs from local wages, and only uses dynamic model to estimate fixed costs and sales • Bajari, Benkard, and Levin (2007) and Pakes, Ostrovsky, and Berry (2007) are methodological papers that incorporate a similar idea Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Section 5 Example: Dunne et al. (2013) Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Dunne et al. (2013) “Entry, Exit and the Determinants of Market Structure” I • Market structure = number and relative size of firms • Classic question in IO: how does market structure affect competition? • Here: how is market structure determined? Entry and exit • Sunk entry costs • Fixed operating costs • Expectations of profits (nature of competition) • Like Bresnahan and Reiss (1991) summarize with profits as a function of number of firms, π(n) • Estimate dynamic model of entry and exit to determine relative importance of factors affecting market structure • Context: dentists and chiropractors Dynamic Oligopoly Model I Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References • Similar to Pakes, Ostrovsky, and Berry (2007) • State variables s = (n, z) • n = number of firms, z = exogenous profit shifters • Follow a finite state Markov process • Parameters θ • Profit π(s; θ) (leave θ implicit henceforth) • Fixed cost λi ∼ Gλ • Discount factor δ • Value function V(s; λi ) = π(s) + max{δVC(s) − δλi , 0} where VC is expected next period’s value function [ [ ] ] VC(s) =Ecs′ π(s′ ) + Eλ′ max{δVC(s′ ) − δλ′ , 0}|s |s Dynamic Oligopoly Model II Paul Schrimpf Introduction • Probability of exit: Model Identification px (s) = P(λi > VC(s)) = 1 − Gλ (VC(s)). Estimation Example: Dunne et al. (2013) Generalizations and extensions References • Assume λ exponential, Gλ = 1 − e−(1/σ )λ , then [ ( ) ] VC(s) = Ecs′ π(s′ ) + δVC(s′ ) − δσ 1 − px (s′ ) |s • Let Mc be the transition matrix, then VC =Mc [π + δVC − δσ (1 − px )] VC =(I − δMc )−1 Mc [π − δσ (1 − px )] (1) • Pakes, Ostrovsky, and Berry (2007): use non parametric estimates of Mc and px in (1) to form VC Dynamic Oligopoly Model III Paul Schrimpf Introduction Model • Here: use non parametric estimate of Mc and form VC by solving Identification [ ] VC = Mc π + δVC − δσ Gλ (VC) Estimation Example: Dunne et al. (2013) Generalizations and extensions References • Potential entrants: • Expected value after entering [ ( ) ] VE(s) = Ees′ π(s′ ) + δVC(s′ ) − δσ 1 − px (s′ ) |s • Cost of entry κi ∼ Gκ • Entry probability pe (s) = P (κi < δVE(s)) = Gκ (δVE(s)) • As before can use Bellman equation in matrix form to solve for VE Dynamic Oligopoly Empirical specification I Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions • Data: U.S. Census of Service Industries and Longitudinal Business Database • 5 periods – 5 year intervals from 1982-2002 • 639 geographic markets for dentists; 410 for chiropractors • Observed average market-level profits πmt • Number of firms nmt , entrants, emt , exits xmt , potential entrants pmt • Market characteristics zmt = (popmt , wmt , incmt ) References • Profit function 5 ∑ πmt =θ0 + θk 1{nmt = k} + θ6 nmt + θ7 n2mt + k=1 + quadratic polynimal in zmt + + fm + εmt Key assumption: εmt independent over time Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Empirical specification II • Transition matrix Mc • Define ˆ zmt = estimate value polynomial in zmt in profit function • Discretize ˆ zmt into 10 categories and use sample averages to estimate transition probabilities • Fixed (Gλ ) and entry costs (Gκ ) c ) and VE(σ c ) as described above • VC(σ • Log-likelihood ( ( )) c mt (σ ); σ + (nmt − xmt ) log Gλ VC ( ( )) c mt (σ ); σ + ∑ +xmt log 1 − Gλ VC ( ( )) L(σ , α) = κ c +e log G VE (σ ); α + mt mt m,t ( ( )) c mt (σ ); α +(pmn − emt ) log 1 − Gκ VE Dynamic Oligopoly Results Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Profit function: • Decreasing with n increasing in w, inc, pop • Compare fixed effects and OLS estimates in depth • Seems unneeded to me; there is no reason you want to use the OLS estimates anyway • More relevant concern is assumption of εmt independent over time — this is empirically testable, but they do not do anything about it Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References ˆ π(n) Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Dynamic Oligopoly Subsidies to entry and fixed costs Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) • Health Professional Shortage Areas (HPSA) have entry Generalizations and extensions • Entry cost subsidy = change distribution of entry costs References subsidies for all markets to the distribution estimated for HPSA markets • Fixed cost subsidy = reduce mean of fixed cost by 8% (chosen to generate similar number of firms as HPSA subsidy) Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References 2 2 FIXME: The numbers in this table are different in the published paper. Chiro estimates look the same, but dentists changed. Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Section 6 Generalizations and extensions Dynamic Oligopoly Paul Schrimpf Generalizations and extensions Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References • Unobserved state variables • Multiple equilibria • Continuous time • Non-additively separable preferences over-time (such as Epstein-Zin preferences) Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Ackerberg, D., K. Caves, and G. Frazer. 2006. “Structural identification of production functions.” URL http://mpra.ub.uni-muenchen.de/38349/. Aguirregabiria, Victor. 2012. “Empirical Industrial Organization: Models, Methods, and Applications.” URL http://www.aguirregabiria.org/barcelona/book_ dynamic_io.pdf. Aguirregabiria, Victor and Chun-Yu Ho. 2012. “A dynamic oligopoly game of the US airline industry: Estimation and policy experiments.” Journal of Econometrics 168 (1):156 – 173. URL http://www.sciencedirect.com/science/ article/pii/S030440761100176X. Aguirregabiria, Victor and Pedro Mira. 2007. “Sequential Estimation of Dynamic Discrete Games.” Econometrica 75 (1):pp. 1–53. URL http://www.jstor.org/stable/4123107. Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References ———. 2010. “Dynamic discrete choice structural models: A survey.” Journal of Econometrics 156 (1):38 – 67. URL http://www.sciencedirect.com/science/article/ pii/S0304407609001985. Bajari, Patrick, C. Lanier Benkard, and Jonathan Levin. 2007. “Estimating Dynamic Models of Imperfect Competition.” Econometrica 75 (5):pp. 1331–1370. URL http://www.jstor.org/stable/4502033. Bajari, Patrick, Victor Chernozhukov, Han Hong, and Denis Nekipelov. 2009. “Nonparametric and Semiparametric Analysis of a Dynamic Discrete Game.” Tech. rep. URL http://www.econ.yale.edu/seminars/apmicro/am09/ bajari-090423.pdf. Bresnahan, Timothy F. and Peter C. Reiss. 1991. “Entry and Competition in Concentrated Markets.” Journal of Political Economy 99 (5):pp. 977–1009. URL http://www.jstor.org/stable/2937655. Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Doraszelski, Ulrich and Ariel Pakes. 2007. “Chapter 30 A Framework for Applied Dynamic Analysis in IO.” In Handbook of Industrial Organization, Handbook of Industrial Organization, vol. 3, edited by M. Armstrong and R. Porter. Elsevier, 1887 – 1966. URL http://www.sciencedirect. com/science/article/pii/S1573448X06030305. Doraszelski, Ulrich and Mark Satterthwaite. 2010. “Computable Markov-perfect industry dynamics.” The RAND Journal of Economics 41 (2):215–243. URL http://onlinelibrary.wiley.com/doi/10.1111/j. 1756-2171.2010.00097.x/full. Dunne, Timothy, Shawn D. Klimek, Mark J. Roberts, and Daniel Yi Xu. 2013. “Entry, exit, and the determinants of market structure.” The RAND Journal of Economics 44 (3):462–487. URL http://dx.doi.org/10.1111/1756-2171.12027. Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Ericson, Richard and Ariel Pakes. 1995. “Markov-perfect industry dynamics: A framework for empirical work.” The Review of Economic Studies 62 (1):53–82. URL http:// restud.oxfordjournals.org/content/62/1/53.short. Gowrisankaran, Gautam. 1999. “A dynamic model of endogenous horizontal mergers.” The RAND Journal of Economics :56–83URL http://www.jstor.org/stable/10.2307/2556046. Holmes, T.J. 2011. “The Diffusion of Wal-Mart and Economies of Density.” Econometrica 79 (1):253–302. URL http://onlinelibrary.wiley.com/doi/10.3982/ ECTA7699/abstract. Hotz, V. Joseph and Robert A. Miller. 1993. “Conditional Choice Probabilities and the Estimation of Dynamic Models.” The Review of Economic Studies 60 (3):pp. 497–529. URL http://www.jstor.org/stable/2298122. Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Magnac, Thierry and David Thesmar. 2002. “Identifying Dynamic Discrete Decision Processes.” Econometrica 70 (2):801–816. URL http: //www.jstor.org.libproxy.mit.edu/stable/2692293. Pakes, Ariel, Michael Ostrovsky, and Steven Berry. 2007. “Simple Estimators for the Parameters of Discrete Dynamic Games (With Entry/Exit Examples).” The RAND Journal of Economics 38 (2):pp. 373–399. URL http://www.jstor.org/stable/25046311. Pesendorfer, Martin and Philipp Schmidt-Dengler. 2008. “Asymptotic Least Squares Estimators for Dynamic Games1.” Review of Economic Studies 75 (3):901–928. URL http: //dx.doi.org/10.1111/j.1467-937X.2008.00496.x. Dynamic Oligopoly Paul Schrimpf Introduction Model Identification Estimation Example: Dunne et al. (2013) Generalizations and extensions References Su, C.L. and K.L. Judd. 2012. “Constrained optimization approaches to estimation of structural models.” Econometrica 80 (5):2213–2230. URL http://onlinelibrary.wiley.com/doi/10.3982/ ECTA7925/abstract.
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