an empirical model of firm entry with endogenous product...
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Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
An empirical model of firm entry withendogenous product-type choicesSeim(2006), RAND Journal of Economics
Wooyong Lee
31 Jan 2013
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Introduction
Before : entry model, identical products
In this paper : entry with simultaneous location choice
Before or some other papers : complete info game
In this paper : incomplete info game
(greatly reduces computational burden)
Results : video retail industry location data
firms differentiate to shield profit from competitionmore scope for product differentiation → more marketpower (more entry)
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Outline
1 Summary of the paperModelEstimationData and Result
2 Contribution and weakness of the paperContribution: Endogenized product-quality choiceContribution: Incomplete information on profitsWeakness of the paper
3 Suggestions for further research
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Section 1
Summary of the paper
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Model Setup
market m = 1, 2, . . . ,M
let’s focus on one market m:(script m removed for ease of exposition)
location l = 0, 1, . . . ,Lfirm f = 1, 2, . . . ,Fdecision df = (dfl )Ll=0 ∈ {0, 1}L+1
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Model Setup
payoff Πfl = Xlβ + ξ + h(Γ.l ,n) + εfl
X : observable market characteristics
ξ : unobservable market characteristics, known to firms
h() : effect of competition on profits; specified later
Γ.l : interaction between l and 1 through Ln = (nl )
Ll=1 : number of firms at location l
εfl : idiosyncratic profitability of firm f at location l
Πf 0 normalized to 0
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Assumptions
Assumption (Independent symmetric private values)
ε1, . . . , εF are private information to the players and areindependently and identically distributed draws from thedistribution G (·)
Assumption (Additively separable competitors’ effects)
h(Γ.l ,n) =∑L
k=1 γkl nk
Assumption (Distance bands)
let dkl be the distance between location k and l.γkl = γk ′l = γb if Db ≤ γkl , γk ′l < Db+1, where Db and Db+1
denote cutoffs that define a distance band.
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Assumptions
Under distance bands b = 0, 1, . . . ,B, with correspondingcutoff points Db and Db+1 where D0 = 0, the resulting payofffunction is given by
Πfl = Xlβ + ξ +∑
b γbNbl + εfl
γb : competitive effect in distance band b
Nbl =∑
k Ibkl nk : number of firms in distance band b
Ibkl := I(dkl ∈ [Db,Db+1)), I(·) : indicator function
nk : number of firms at location k
E :=∑
b Nbl : total number of firms in the market
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Conjectures and equilibrium
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Conjectures and equilibrium
Given the expected competitor distribution across marketlocations, firms calculate its expected profit at each location l :
E(Πfl ) = Xlβ + ξ +∑
b γbE(Nbl ) + εfl
:= E(Π̄fl ) + εfl
note that E(Nbl ) =∑
k IbklE(nk )
Structure of the game :
1 firms decide whether or not to enter → E determined
2 Given number of firms E , firms decide locations
→ solve backward
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Conjectures and equilibrium
Due to the symmetry of rival’s types, firm f ’s perception offirm g ’s location strategy is the same for all competitors.
Let θ1 = (β, γ). Given ξ,X, E , θ1, the probability thatcompetitor g chooses location l is given by
pgl (ξ,X,E, θ1)
= P(E(Π̄gl ) + εgl > E(Π̄gk ) + εgk ∀k 6= l , ∀g 6= f )
Expected number of competitors at location k is
E(nk ) = (E − 1)pgk
E(Nbl ) =∑
k IbklE(nk ) =
∑k Ib
kl (E − 1)pgk + I(b = 0)
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Conjectures and equilibrium
Assumption
ε are i.i.d. draws from a type 1 extreme-value distribution withscale parameter normalized to one.
By this assumption, there exists a closed-form formula for pgl :
pgl =exp{E(Π̄gl )}∑L
k=1 exp{E(Π̄gk)}
Since types are symmetric, every firm has the same equilibriumconjecture of its competitors’ location choices :
pg := (pgl )Ll=1 = pf = p∗ := (p∗l )Ll=1
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Conjectures and equilibrium
A firm’s vector of equilibrium conjectures over all locations l isdefined by
p∗l =exp{E(Π̄l (X,p
∗, E , θ1))}∑Lk=1 exp{E(Π̄k (X,p∗, E , θ1))}
=exp{Xlβ + γ0 + (E − 1)
∑b γb
∑j Ib
jl p∗j }∑L
k=1 exp{Xkβ + γ0 + (E − 1)∑
b γb∑
j Ibjk p∗j }
for all l = 1, . . . ,L
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Conjectures and equilibrium
let’s analyze E :
In equilibrium, each entrant earns nonnegative profits inexpectation, while any additional entrant would sufferlosses.
The probability of entry by a firm into a market involves acomparison of a weighted average of payoffs acrosslocations to the normalized payoff of not entering.
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Conjectures and equilibrium
Given the assumption of i.i.d. type 1 extreme-valueprofitability types,
P(entry) =exp(ξ)
∑Ll=1 exp{E(Π̄l (X,p
∗, E , θ1))}1 + exp(ξ)
∑Ll=1 exp{E(Π̄l (X,p∗, E , θ1))}
Since the probability of entry is identical acrosscompetitors,
E = F × P(entry)
Ways to choose F : 50% enter the market, F = 50
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Estimation : Econometric Specification
Assumption
The expected number of entrants predicted by the modelexactly equals the number of entrants observed in the data.
With E being the observed number of entrants, by the entryprobability equation,
ξ = ln E − ln(F − E)− ln( L∑
l=1
exp{E(Π̄l (X,p∗, E , θ1))}
)
Assumption
ξm are i.i.d. random draws from a Normal distribution withparameter θ2 = (µ, σ) and independent of ε.
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Likelihood
Data from market m = 1, . . . ,M
Each market is treated as an independent Fm-playerlocation game
dm = (dm1 , . . . , d
mF ) : vector of actions taken by Fm
players in market m
The likelihood function is given by
L(θ1, θ2) =M∏
m=1
pθ1(dm|ξm,Xm, Em)gθ2(ξm|Xm, Em,Fm)
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Estimation Procedure
1 initialize (θ1, θ2)
2 given (θ1, θ2), (Xm)Mm=1, F , (Em)M
m=1, solve equilibriumconjecture equation for pm for each m separately
3 calculate ξm with pm, (θ1, θ2), (Xm)Mm=1, F , (Em)M
m=1 foreach m
4 estimate (θ1, θ2) by maximizing likelihood function
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Estimation Issues
initial value : a grid search over the parameter space
likelihood maximization : Nelder-Mead optimizationalgorithm
problematic when there are multiple equilibria : appendixproves uniqueness for two distance bands with fourlocations, simulation evidence suggests further result
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Data description
video retail industry
videotapes are standardized; main differentiation by storelocation
isolated markets; no large city nearby, no metropolitan area
exclude tourist regions
locations by Census tracts
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Data description
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Data description
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Data description
d0 = 0.5 miles, d1 = 3 miles
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Data description
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Estimation Result
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Estimation Result
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Simulation Result
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Simulation Result
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Section 2
Contribution and weakness of the paper
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Previous Works
focused on tradeoff between demand and intensity ofcompetition
Early works on product quality differentiation :Hotelling(1929), Lancaster(1966,1979)
(competition on characteristic space)
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Model for Endogenized Product Choice
Empirically tractable model of competition oncharacteristic space (tractable for large L)
Unisolated market : locations affect each other viadistance
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Empirical Results
Firms differentiate to shield from competition
More scope for product differentiation → more marketpower(more entry)
More disperse population → less gain fromdifferentiation(slightly more entry in total)
The two offset each other in video retail industry data
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Previous Works
Complete information game → computational burden
→ Limited number of locations
Mazzeo(2002) : entry with product-quality choice,complete information game
→ uses motel industry data, computation is burdensomewith 3 locations
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Incomplete Information Game
Introduce private information : idiosyncratic profitability
sources: cost, intangible assets, customer service,inventory maintenance etc.
As Rust(1994) notes : Bayesian Nash equilibriumconjectures are easy to derive
Other works under information asymmetry :
Aguirregabiria and Mira(2006), Pakes, Ostrovsky andBerry(2005), Pesendorfer and Schmidt-Dengler(2003)
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Cost of Assumptions
Distance band approach :
All locations with same distance band have the sameimpact
two at the north � one at the north and one at the south
ε being i.i.d. type 1 extreme value distribution :
idiosyncratic profitability uncorrelated across firms at alocation, across location for a firm
no spatial correlation
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Possible Issues
When there are multiple equilibria :
matching location probabilities to observed locationchoices is problematic
uniqueness for general setting is only verified by simulation
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Section 3
Suggestions for further research
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Further research so far
entry game with multistore/multiproduct firms (Jia 2008)
dynamic entry game
timing game (Sweeting 2009)
estimation with multiple equilibria (Aguirregabiria 2012 :identical product case)
estimation in case of location heterogeneity(Aguirregabiria 2012)
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Further research so far
estimation of demand system by quantity, price data ofstores : Wang(2010)
effect of other factors on entry decisions: regulation(Gowrisankaran and Krainer 2011), organizationalstructure (Takechi and Higashida 2012), managerial ability(Goldfarb and Xiao 2011)
Seim(2006)
Wooyong Lee
Summary
Model
Estimation
Result
Contributionand Weakness
Product
Information
Weakness
Suggestions
Suggestions
nonlinear effect of additional entrant
relaxing distance band assumption
investigation of conditions for unique equilibrium