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时间:2014-02-19    浏览量:2138

Ajay Agrawal, Avi Goldfarb, Florenta Teodoridis. 2013. Does knowledge accumulation increase the returns to collaboration?. Working Paper 19694. National Bureau of Economic Research


Abstract:We conduct the first empirical test of the knowledge burden hypothesis, one of several theories advancedto explain increasing team sizes in science. For identification, we exploit the collapse of the USSR asan exogenous shock to the knowledge frontier causing a sudden release of previously hidden research.We report evidence that team size increased disproportionately in Soviet-rich relative to -poor subfieldsof theoretical mathematics after 1990. Furthermore, consistent with the hypothesized mechanism,scholars in Soviet-rich subfields disproportionately increased citations to Soviet prior art and becameincreasingly specialized.


数据来源:本文研究了1970-201041年间理论数学领域的期刊发表数据。数据库为美国数学社会数据库American Mathematical Society)。

研究方法:工具变量法(以“苏联解体”这一事件为工具变量,与知识前沿扩张有关,同时与合作率变化无关);双重差分模型(difference-in-differences model)以“团队规模”为因变量。以“苏联历史上在该领域是否占优势”为0-1虚拟变量,代表了知识前沿受冲击的程度。以“铁幕是否结束”为0-1虚拟变量,代表了苏联解体前后的两个时期。

Discussion and conclusion:We report evidence that an outward shift in the knowledge frontier is associated witha subsequent increase in research team size and researcher specialization. Importantly, thisevidence is consistent with the knowledge frontier explanation but not the other explanationsfor the widely documented increase in team size. In other words, although this evidence isnot intended to (and does not) rule out the possibility that the other explanations also playa role, it suggests that the knowledge frontier hypothesis is a plausible explanation for atleast some of the observed increase in team size in science.

In our setting, a back-of-the-envelope calculation indicates that the knowledge frontiereffect accounts for 24% of the increase in team size in Soviet-rich fields in theoretical mathematics. We calculate this as follows: team size in Soviet-rich fields increased by 33%, from1.34 to 1.78, in the before versus after period. We estimate that the Soviet-rich fields experienced an 8% disproportionate increase (relative to Soviet-poor) during this period (Table 3,Column 1). This represents 24% of the overall percentage increase. While this rough calculation can be seen as a lower bound because it assumes none of the increase in Soviet-poorsubfields was due to an outward shift in the knowledge frontier, we resist this interpretationbecause of the numerous other assumptions underlying the 24% value.

More broadly, it is important to clarify the limitations of our test of the knowledge burdenhypothesis. First, we test a particular implication of the knowledge burden hypothesis: theimpact of a sudden outward shift in the knowledge frontier on collaboration and specialization. An underlying assumption of this interpretation of our estimates is that the team sizeresponse to a shock is similar to that for a gradual outward shift in the knowledge frontier.However, that may not be the case. Researchers may be able to absorb gradual increases inthe knowledge frontier in a manner that does not generate as high returns to collaboration asthose resulting from a sudden shock that may be more costly for researchers to internalize.Thus, our empirical results may not measure the impact of a gradual shift in the knowledgefrontier.

Second, there may have been other impacts of the collapse of the Soviet Union on the field of mathematics. Borjas and Doran (2012, 2013a, 2013b) emphasize the labor marketimpact of increased competition from Soviet scholars. This increased competition also mayhave driven an increase in collaboration if, for example, returns to collaboration increaseddue to reasons such as risk mitigation (diversification of research projects). While we viewour results on Japanese publications, citations to Soviet prior art, and specialization as moreconsistent with the knowledge burden hypothesis, we cannot definitively reject the possibilitythat changing labor markets also played a role.

Third, we focus on one particular field: mathematics. Adams et al (2005) show thatmathematics is somewhat of an outlier in team size relative to other disciplines in havingrelatively small teams. In the first year of their study, 1981, mathematics publicationshad the fewest number of authors (of 12 fields). Furthermore, mathematics had the lowestannual growth rate in team size from 1981 to 1990 and the second lowest from 1990 to 1999.In contrast, physics and astronomy had the highest growth rates, which likely was at leastpartly driven by the increasing role of capital-intensive equipment (e.g., particle accelerators)in those fields. Therefore, even if 24% is a reasonable lower-bound estimate of the fractionof the percentage increase in team size caused by an outward shift in the knowledge frontierin mathematics, it may be an overestimate in fields where capital equipment plays a morecentral role.

Overall, we document that the knowledge shock caused by the exogenous collapse ofthe Soviet Union led to a disproportionate increase in collaboration among non-Soviet researchers in those subfields in which Soviet mathematicians were strongest relative to othersubfields of theoretical mathematics. Our examination of citations to Soviet prior art, specialization, and team sizes in Japan provides further evidence consistent with the burdenof knowledge hypothesis: a knowledge shock leading to increased specialization and collaboration. In a series of papers (2009, 2010, 2011), Jones presents a variety of interventionsthat are potentially welfare-enhancing in the presence of a knowledge frontier effect. Theseinclude subsidies and rewards to incentivize entry into research careers, team-based evaluation of grant applications, and national or regional subsidies and specialization to preventpoverty traps due to underinvestment in human capital from coordination failures arisingfrom thin markets for complementary skills. Although our study offers no means by which tocomment on the suitability of these interventions to particular policy settings, the evidencewe present here does suggest that the knowledge frontier effect is worthy of further researchand possibly policy attention.





第三,我们聚焦于一个特别的领域:数学。Adams et al的研究展示了相对于其他限制而言,相对小的团队规模对于数学而言并没有显著影响。在他们研究的第一年,1981年,数学刊物在12个研究领域中作者最少。另外,从1981年到1990年,数学研究团队规模的年增长率最低;从1990年到1999年则第二低。相反,物理学和天文学的研究团队规模有着最高的增长率,这一现象可能至少受到了资金密集型的设备的部分影响(如粒子加速器)。因此,尽管24%是对知识前沿向外扩张所带来的影响的粗略计算,在一些资金设备发挥主导作用的领域,它也可能被高估了。


By 苏小舟

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