Globalization and the Gains from Variety Christian Broda David E.Weinstein.
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Transcript of Globalization and the Gains from Variety Christian Broda David E.Weinstein.
Globalization and the Gains from Variety
Christian Broda
David E.Weinstein
Introduction
• Krugman(1979):how countries could gain from trade through the import of new variety
• But no one has estimated the impact of increased variety on aggregate welfare
• This paper try to answer the question how much increases in traded varieties matter for United States: varieties arise threefold in the last 30 years
Method
• Step 1:estimate elasticities of substitution among goods at various levels of aggregation
• Step 2:use these estimated parameters to construct import price index
• Step 3:use the price to obtain an estimate of gains from new imported varieties
Prior work
• Hausman(1981) 试图计算新产品减价对福利的影响,这种方法不适用于计算产品总价格指数
• 研究总体层面的文章都利用数值模拟,这些研究不关注多样化如何影响价格,而是关注潜在福利的变化
• 所有以上研究没有提供如何从理论跨越到实证的第一步,而且需要多种限制性假设
• 假设不同产品的所有品种替代弹性是相同的;假设产品之间的替代弹性与同一产品不同种类之间的替代弹性相同;假设所有种类所有产品的替代弹性相同
• 另外使用数值模型需要小心选择参数和效用函数形式,而本文中所有的参数都是通过回归得到的
• Anderson(1979) 利用双边贸易流对贸易成本和控制变量回归,贸易成本系数为替代弹性。这种方法假设贸易成本全部转嫁给消费者,而且贸易成本不随进口需求的变化而改变,该假设是不符合美国实际情况的。
The definiton of variety
• Krugman(1980) adopted a definition of variety that is based on firm level exports
• This paper use the same definition of variety as in Feenstra(1994)-----a seven or ten digit good produced in a particular country. For example, a good “red wine”, a variety “French red wine”
• The definition highlights an important difference between monopolistic competition models and comparative advantage model:
• In comparative advantage model, consumers are indifferent about where a good is produced as long as the price does not vary, the elasticity of substitution among varieties is infinite
• In monopolistic competition model, the elasticity of substitution among varieties is finite
• If the elasticity of substitution is large ,the gains from varieties is small; low elasticity of substitution across varieties are a necessary condition for potential gain
• In Krugman model there are two channels for the gains from trade arising from variety growth: trade costs fall ;the size of the foreign country rise
• In comparative advantage model, all gains from are achieved through price change
• We choose Dixit and Stigiltz(1977) SDS framework
• CES utility function is easy to estimate
• Helpman and Krugman(1985) model is not easy to create aggregate price index
DATA
• A variety is defined as the import of a particular good from a particular country
• In 1972 the share of import of goods in GDP is 4.8%,in 2001 the share increased to 11.7%
• There has been a dramatic increase in the number of countries supplying each individual good ( table 1,table 2 & table 3 )
• 提供产品的国家增多与全球化以及国家间产品差异是相联系的
• 如果国家之间的产品存在差异,那一定是因为多样化可以带来收益
• 高增长率的国家如韩国、中国提供给美国的产品种类迅速上升,也说明自由化对发展中国家的作用很大
• Eaton 等 (2004) 利用引力模型研究了产品多样化、经济增长和贸易之间的关系
Empirical Strategy
• The Feenstra price index
• Identification and estimation of the elasticity of substitution
The Feenstra price index
• Build an exact aggregate price index corresponding to CES utility function
• Three level utility function:• (1)aggregate imported goods into composite imported
goods (variety-category)• (2)aggregate these imported good into a composite
import good (category-imported good)• (3)combine this imported good with the domestic
good to produce utility
• The upper level utility function(1)
• The composite imported good(2)
• The third level(3)
1)1()1( )( ttt MDU
1)1( )(
Gggtt MM
• The minimum unit cost function of subutility function
• If ,then increase
will lead to unit cost falling• The minimum unit cost function of(2) is
)1(11 ))),(((
Gg
gtgtMgt
Mt dI
• The overall price index is
1111 )()( M
tDtt pp
• Proposition 1:the exact price index for good g with change in varieties is
• Where
• Where capture the role of the new and
disappearing varieties. Is the conventional price index
• It implies that the higher the expenditure share of new varieties ,the lower is and the smaller is the exact price index relative to the conventional price index
• It implies that an increase in the number of varieties lead to a fall in the exact price index relative to the conventional price index
MgP
• Proposition 2:the exact aggregate import price index with variety change is
• Where is the conventional
Import price index , is import bias
1
1
1111
)(
),(
),(),,,,(
ggtw
gt
gt
Gg
tMt
tMt
ttttM
ICIPI
dI
dIIxxPP
gtwgg
GgIPICIPI )()(
• The overall index is
• 以前的指标直接用 代替 ,会导致很大的偏差,如新产品的消费量只占消费量很小的一部分,那么旧的指标会放大新产品的作用
• 该方法消除了对称性误差,不同产品的同幅度价格调整对消费者而言是不同的,因为 是可以变化的
Mt
Dt
wM
w
Dt
Dt
p
p
1
Identification and estimation of the elasticity of substitution
Using a simple model of import demand and supply equations to estimate this elasticity of substitution.
Demand equation is derived from equation(3)
Supply equation is
• Using shares instead of quality ,the demand and supply function are:
• After some calculation, we get equation(18)
• where
gctgctg
ggtgct sp
ln1
ln
gctgctk
gctk
gctk
gctk uspsp )lnln()ln()ln( 2
21
2
)1)(1(1
gg
g
)1)(1(
)2(12
gg
gg
Result
• Estimate strategy involves four stages
• Step1:estimate using (20)
• Step2:calculate for every good g
• Step3:calculate the exact price index using(11)
• Step4:estimate the movement of the aggregate price of imports using equation(12)
Elasticity of substitution
• As we disaggregate, varieties are increasingly substitutable
• Goods with high elasticity of substitution to correspond to goods that we think of as less substitution
• Goods traded on organized exchanges have higher elasticity than those that are not
• (see table IV & V)
The reasonableness of the estimates
• Rauch (1999) divided goods into three categories: commodities ,reference priced goods and differentiated goods
• Commodities are probably correlated with more substitutable goods
• Estimate at the four digit level to make them directly comparable with Rauch (1999) ,see table VI
Growth in varieties
• 计算 中的一个困难:在 时 没有定义,解决方法是, 7 位代码或 10 位代码中新增加的一个种类的替代率为,在同一个 5 位代码类型中其他商品和种类的替代率的加权平均
• 计算结果见表 VII
Import prices and welfare
• Aggregate exact price index 估计结果 (tabel VII)• 价格在 1972-1988 年下降了 19.7 %,在 1990-20
01 年下降了 8.3 %• 后期价格下降速度减慢说明从东南亚贸易中得到
的收益是在 90 年代之前得到的• 由于之前没有类似的文献以证明结论的正确性,
利用一个 CPI 指数的研究从侧面类比。该研究指出 CPI 价格指数高估了生活成本 1.2 %,这种误差来源于产品数量的变化。因此,如果采用传统的 unaccounted variety growth 得到的误差会很大
• 福利效应的计算采用 Krugman(1980) 框架,结果显示消费者愿意利用他们收入的 2.6 %去得到 2001 比 1972 年多的产品种类
Robustness
• 和之前的研究不同,本文允许不同种类产品的消费份额是不同的,另外不同产品的替代弹性不同,各个市场的供给弹性也不同
• 消费份额相同、替代弹性相同都会高估多样化带来的福利效应
• 放松 CES 效用函数假设,利用二次方程效用函数仍然可以得到类似的结论
• 文中假设所有产品都是最终消费品,但是实际情况不是如此,特别是资本品在长期是会扩大产品多样化带来的收益,因此将资本品当作最终产品计算会低估福利效应
• 在 Krugman 的生产函数中,国内产品种类的变化不会影响国外产品,利用 Helpman and Krugman(1985) 模型,外国产品进入会导致国内部门萎缩转向非贸易部门。在一定的参数假设下,从国外引入一个品种会取代 0.16 个国内品种,因此会把福利降低 16 %