Practical operation and theoretical basis of difference-in-difference regression in science of science:The comparative trial on the scientific performance of Nobel laureates versus their coauthors

Purpose:In recent decades,with the availability of large-scale scientific corpus datasets,difference-in-difference(DID)is increasingly used in the science of science and bibliometrics studies.DID method outputs the unbiased estimation on condition that several hypotheses hold,especially the common trend assumption.In this paper,we gave a systematic demonstration of DID in the science of science,and the potential ways to improve the accuracy of DID method.Design/methodology/approach:At first,we reviewed the statistical assumptions,the model specification,and the application procedures of DID method.Second,to improve the necessary assumptions before conducting DID regression and the accuracy of estimation,we introduced some matching techniques serving as the pre-selecting step for DID design by matching control individuals who are equivalent to those treated ones on observational variables before the intervention.Lastly,we performed a case study to estimate the effects of prizewinning on the scientific performance of Nobel laureates,by comparing the yearly citation impact after the prizewinning year between Nobel laureates and their prizewinning-work coauthors.Findings:We introduced the procedures to conduct a DID estimation and demonstrated the effectiveness to use matching method to improve the results.As a case study,we found that there are no significant increases in citations for Nobel laureates compared to their prizewinning coauthors.Research limitations:This study ignored the rigorous mathematical deduction parts of DID,while focused on the practical parts.Practical implications:This work gives experimental practice and potential guidelines to use DID method in science of science and bibliometrics studies.Originality/value:This study gains insights into the usage of econometric tools in science of science.

Does the Environmental Supervision System Improve Air Quality in China?An Empirical Study using the Difference-in-Differences Model

To effectively solve the problem of environmental pollution,the Chinese government has implemented an environmental supervision system since 2002.The environmental supervision system mainly uses the four functions of supervision,investigation,coordination,and emergency response to strengthen environmental protection supervision and law enforcement,respond to environmental emergencies,and coordinate cross-regional pollution disputes.As an important system design for China to control environmental pollution and promote the ecological transformation of economic development,the policy effect of the environmental supervision system deserves attention.This paper uses the difference-in-differences method to investigate the impact of the top-down environmental supervision system on air quality based on the 2000-2016 data for 285 prefecture-level cities in China.The results indicate that the annual average concentration of PM_(2.5)decreased significantly after the implementation of the environmental supervision system.The dynamic analysis shows that PM_(2.5)decreased most markedly in the first year after the implementation of the policy,and then the effect gradually weakened.Mechanism analysis suggests that the environmental supervision system can break the collusion between government and enterprise,encourage enterprises to carry out technological innovation,change pollutant discharge behavior and push local governments to adjust the industrial structure,enhance environmental protection awareness to reduce the PM_(2.5)concentration,and improve air quality.Comparing different regions,the PM_(2.5)in East China,North China and Northeast China are relatively high,and the pressure for air pollution control is great.Meanwhile,we find that the environmental supervision system has a significant station effect.Compared with other cities,the cities where the environmental supervision centers are located are more deterred by the environmental supervision,and their air quality has improved to a significantly greater degree.In the future,we should further strengthen the environmental supervision of high-pollution areas and non-station cities,and pay more attention to improving the long-term effect of the environmental supervision system.

Promoting grain production through high-standard farmland construction:Evidence in China

Food security is a strategic priority for a country’s economic development.In China,high-standard farmland construction(HSFC)is an important initiative to stabilize grain production and increase grain production capacity.Based on panel data from 31 sample provinces,autonomous regions,and municipalities in China from 2005–2017,this study explored the impact of HSFC on grain yield using the difference-in-differences(DID)method.The results showed that HSFC significantly increased total grain production,which is robust to various checks.HSFC increased grain yield through three potential mechanisms.First,it could increase the grain replanting index.Second,it could effectively reduce yield loss due to droughts and floods.Last,HSFC could strengthen the cultivated land by renovating the low-and medium-yielding fields.Heterogeneity analysis found that the HSFC farmland showed a significant increase in grain yield only in the main grain-producing areas and balanced areas.In addition,HSFC significantly increased the yields of rice,wheat,and maize while leading to a reduction in soybean yields.The findings suggest the government should continue to promote HSFC,improve construction standards,and strictly control the“non-agriculturalization”and“non-coordination”of farmland to increase grain production further.At the same time,market mechanisms should be used to incentivize soybean farming,improve returns and stabilize soybean yields.

Are cities greener because of innovation?Independent innovation policy and green economic efficiency

The national independent innovation demonstration zone(NIIDZ)is an independent innovation policy that plays a crucial role in implementing strategies.Given the importance of the NIIDZ,this study uses panel data of 278 prefecture-level cities in China from 2006 to 2020 and empirically examines the effect and internal mechanism of the NIIDZ on green economic efficiency(GEE)using the difference-in-difference model(DID).The results show that the NIIDZ effectively enhances the growth of GEE,and the results remain valid through several robustness tests,such as year-by-year propensity score matching.The transmission mechanism suggests that the NIIDZ indirectly drives GEE by accelerating scientific and technological investment,promoting talent concentration,and optimizing the industrial structure.Moreover,heterogeneity analysis reveals that the promotion effect of the NIIDZ on GEE is more prominent in the eastern region and high green development level areas.The study’s findings can serve as a reference for China to further utilize the policy effectiveness of the NIIDZ and accelerate the high-quality development of the green economy in the future.

Impact of an official accountability audit on industrial structure adjustment:a case study of environmental regulation in China

As a unique environmental regulation in China,the official accountability audit was piloted in 2014.With a focus on prioritizing the ecological environment,officials in pilot districts have implemented economic construction,adjusted industrial structures,and promoted coordinated development between the economy and environment.The effects of implementation have garnered widespread attention from society.However,there is limited research on the impact of an accountability audit on industrial structure adjustments.Using the“Accountability Audit of Officials for Natural Resource Assets(Trial)”released in 2015 as a quasi-natural experiment,this study collected panel data from 279 cities between 2013 and 2017.It then empirically analyzed the impact mechanism and effects of the accountability audit on industrial structure adjustment using the Propensity Score Matching and Difference-in-Differences model.The research findings indicate that the accountability audit directly impacted industrial structure adjustment,promoting the upgrading of the primary industry to the secondary industry and restricting the development of the tertiary industry.In addition,the audit is beneficial for enterprise entry,but not conducive to technological innovation,and has no significant impact on foreign direct investment.This conclusion fills a gap in the existing research and provides valuable insights for policymakers.

Do smart city policies improve energy efficiency?Evidence from China

To address air pollution and offer a convenient and comfortable living environment,the Chinese government launched a smart city pilot(SCP)project in 2012,accompanied by a comprehensive set of environmental and energy-related laws and regulations.Although academic interest in smart cities has surged,there remains a notable gap in empirical research exploring the economic,environmental,and energy effects of such initiatives.Taking 232 prefecture-level cities from 2003 to 2017 as research subjects,this study measures energy effi‐ciency by using energy consumption per unit of GDP and adopts a difference-in-differences(DID)analysis to investigate the impact of SCPs on energy efficiency.The empirical results indicate that SCPs improved energy efficiency by promoting urban technological innovation capabilities and green total factor productivity,and this effect was more pronounced in cities that were more dependent on traditional fossil fuel energy sources and had more developed fiscal and financial levels.Studying the impact of smart city construction on energy utilization efficiency in developing countries,such as China,is not only significantly enlightening for China’s green and low-carbon transition but also provides reference opinions for constructing smart cities and the path to enhancing energy efficiency in other developing countries.The findings provide valuable insights into the global development of smart cities,urban sustainability,and high-quality economic growth.

The heterogeneous impact of China-Europe railway express on the efficiency of logistics industry in node cities

Purpose-The spatiotemporal compression effect of China-Europe Railway Express(CR-Express)can reduce the filow costs of resources between China's node cities.Additionally,it can break through the limitations of low-added-value marine products,significantly impacting the logistics industry efficiency.However,there are few literature verifying and analyzing its heterogeneity.This study explores the impact of CR-Express on the efficiency of logistics industry in node cities and analyzes the heterogeneity.Design/methodology/approach-First,this study uses panel data to measure the efficiency of node city logistics industry.Secondiy,this study discusses the impact of the opening of CR-Express on the efficiency of logistics industry in node cities based on the multi-period differential model.Finally,according to the node city difference,the sample city experimental group is grouped for heterogeneity analysis.Findings-The results show that CR-Express can promote the urban logistics industry efficiency,with an average effect of 4.55%.According to the urban characteristics classification,the heterogeneity analysis shows that the efficiency improvement effect of logistics industry in inland cities is more obvious.The improvement effect of node cities and central cities in central and western China is stronger,especially in the sample of megacities and type I big cities.Compared with non-value chain industrial products,the CR-Express has significant promotion effects on the logistics efficiency of the cities where main goods are value chain products.Originality/value-Under the background of double cycle development,this paper can provide a scientific basis for the investment benefit evaluation of CR-Express construction and the follow-up route planning.

Paired Assistance:Policy Rationale and Economic Performance as Illustrated by Xizang and Xinjiang

This study highlights the changing priorities of China’s paired assistance throughout the past decades,as well as its theoretical implications and economic growth effects for recipient regions.Using panel data from 32 prefecture-level cities from 1990 to 2020,this study uses the multiperiod difference-in-differences approach to examine how paired assistance has contributed to economic growth in Xizang Autonomous Region and Xinjiang Uygur Autonomous Region.The findings indicate that,first,the implementation of the paired assistance policy has boosted economic growth in Xizang and Xinjiang.Second,paired assistance has stimulated economic growth in recipient communities by improving infrastructure.Third,paired assistance has contributed to economic growth in recipient communities by providing improved public services such as education and healthcare.Improvements to public services have a relatively smaller indirect effect in short term than infrastructure development on economic growth.Yet both education and healthcare are crucial to people’s quality of life in recipient communities.This paper has refined and broadened research on the effects of paired assistance,providing preference for future policymaking.

The Effects of Infrastructure Projects on House Prices and Rents:Evidence from the HS2 Extension Cancellation in the UK

This paper uses the HS2 extension cancellation in November 2021 as a quasi-experiment to study its impact on house prices and rents in Leeds.Using a DiD approach on repeat sales and monthly rents,I compare property values near the HS2 station and proposed construction site before and after the announcement.Results show a 3.6%decrease in house prices and a 3.9%decline in rents near the station,while properties near the construction site experienced a 2.4%increase in prices and a 2.1%rise in rents.This is the first paper to analyse the HS2 cancellation effect using panel data methods.

The Effect of Urban Agglomeration Expansion on PM_(2.5) Concentrations: Evidence from a Quasi-natural Experiment

This study constructs a quasi-natural experiment based on the expansion of the Yangtze River Delta urban agglomeration(YRDUA) of China in 2010 to investigate the impact and inner mechanism of urban agglomeration expansion on fine particulate matter(PM_(2.5)) concentrations through propensity scores in difference-in-differences models(PSM-DID) using panel data from 286 prefecturelevel cities in China from 2003 to 2016. The results show that 1) urban agglomeration expansion contributes to an overall decrease in PM_(2.5)concentration, which is mainly achieved from the original cities. For the new cities, on the other hand, the expansion significantly increases the local PM_(2.5)concentration. 2) In the long term, the significant influence of urban agglomeration expansion on PM_(2.5)concentration lasts for three years and gradually decreases. A series of robustness tests confirm the applicability of the PSM-DID model.3) Cities with weaker government regulation, a better educated population and higher per capita income present stronger PM_(2.5)reduction effects. 4) Urban agglomeration expansion affects the PM_(2.5)concentration mainly through industrial transfer and population migration, which cause a decrease in the PM_(2.5)concentration in the original cities and an increase in the PM_(2.5)concentration in the new cities.Corresponding policy suggestions are proposed based on the conclusions.

Does innovative city pilot policy promote urban green growth in China?An analysis of green total factor productivity,2005-2020

The innovative city pilot policy(ICPP)is an essential manifestation of China’s construction of an innovative and green-driven development country.We incorporated urban green total factor productivity(GTFP)growth into the evaluation of ICPP.Based on the panel data of 223 cities in China from 2005 to 2020,we used the difference-in-differences model to empirically assess the influence and mechanism of the ICPP on urban GTFP growth.The main results show that(i)The ICPP has maintained an effectively fluctuating promotion on urban GTFP growth,mainly manifested in the urban green technological progress improvement.(ii)The ICPP has urban heterogeneity in promoting GTFP growth in pilot cities,mainly affecting key cities such as provincial capitals.(iii)The interaction between the agglomeration of producer services and the ICPP inhibits GTFP growth in pilot cities.

Promoting or inhibiting? Green fiscal policy and urban green innovation

Can green fiscal policy(GFP)incentivize the proliferation of urban green innovation(GI)and be a novel cata‐lyst for energy conservation and emission reduction within the“dual-carbon”framework?This paper explores GFP ramifications for GI by implementing a difference-in-differences model in a natural experiment centered on the“Comprehensive Demonstration City of Energy Saving and Emission Reduction Fiscal Policies”.The em‐pirical analysis reveals several key findings:(1)GFP exhibits significant augmentation at the GI level,with an observable evolutionary trend of increasing marginal impact.Importantly,these outcomes withstand rigorous robustness tests,including propensity score matching.(2)A mechanism analysis elucidates the dual impact of GFP on GI growth.GFP directly fosters GI advancement indirectly by promoting talent aggregation,expanding scientific and technological investment,and attracting external financial resources.(3)A heterogeneity analy‐sis demonstrates that GFP enhancement of GI is closely associated with the patent category,manifesting a dis‐tinct pattern of“eastern region>other regions”and“non-resource cities>resource cities”.The study’s em‐pirical findings offer crucial real-world insights to guide the Chinese government in formulating a more effi‐cient GFP and facilitating the expansion of innovative endeavors while contributing to environmentally sus‐tainable and high-value development.

The Impact of the Establishment of National High-tech Zones on Total Factor Productivity of Chinese Enterprises

The National High-tech Zone(NHTZs)is an important strategic platform for cultivating high-tech industries and realizing high-quality economic development in China.Based on the combined data from 2006 to 2014 of the industrial enterprise database,the customs database,and the China Development Zones Audit and Announcement Catalogue(abbreviated asthe Catalogue),this paper systematically investigates the influence of the construction of NHTZs on enterprise’s total factor productivity(TFP).Results show that NHTZs have a positive impact on the TFP of enterprises in the zone,and this conclusion is still valid after considering endogeneity problems.Furthermore,the above productivity effects of NHTZs are heterogeneous in terms of enterprise ownership,external environment and establishment time,and NHTZs have greater stimulation effects on enterprise productivity after comparing with other types of functional zones.An investigation of the specific mechanisms at play shows that NHTZs promote the TFP of enterprises in the zone through the release of preferential policies,strengthening the“technology spillover effects”of imported intermediate goods,enhancing enterprise’s innovation ability and attracting talent.In addition,based on the decomposition of industry productivity,this paper also investigates the impact of NHTZs on changes in industry productivity and finds that NHTZs promote the overall productivity of specific industries mainly by stimulating the productivity improvement of incumbent enterprises and expanding the market share of high-productivity enterprises.Moreover,the preferential policies of NHTZs do not significantly stimulate high-productivity enterprises to enter the zones,nor do they cause low-productivity enterprises to exit.This research is helpful in objectively evaluating the economic effects of the NHTZs in China and in providing a theoretical basis for its further adjustment.

Higher Education Admission Policy and Social Class of Ethnic Minority:The Case of Guangxi Zhuang Autonomous Region,China

Gaokao has been considered as the gatekeeper of intergenerational class reproduction in today’s slowing social mobility in China.In order to bolster the fairness of Gaokao,the Policy of Bonus Scores for Ethnic Minority Candidates(PBSEMC)has been issued,whose,however,effectiveness in promoting upward social class has not been adequately empirically explored.The difference-in-differences(DID)analysis based on cross-sectional data,which is distinct from the traditional DID analysis paradigm,was implemented to assess the Reform of PBSEMC in the Guangxi Zhuang Autonomous Region in 1988.The results showed that PBSEMC had a significant and positive impact on the social classes of ethnic minorities,and gender,residence type and occupation type were also relevant to social class,aligning with the previous literature.The PBSEMC is effective in improving the social classes of ethnic minorities.However,the PBSEMC policy should be made more precise,in order to benefit the candidates who are in genuine need of assistance.

Transportation Infrastructure Quality Effect on Economic Growth： Evidence from the China Railway Speed-Up Campaigns

Beginning in 1997, China implemented a six-round campaign to accelerate train service, known as the ＂ China Railway Speed-Up Campaign＇＂ which greatly increased railway capacity and improved the quality of rail facilities. This can be seen as a natural experiment of the effects of improving the quality of transportation infrastructure. Using the Beijing- Guangzhou Line and the Beijing-Shanghai Line as examples, this paper creates city-level panel data for stations along accelerated lines and traditional stations for the years between 1994 and 2006 and systematically examines the campaign＇s effect on economic growth using difference-in-difference （DID） methodology. Our research concludes that railway acceleration has promoted economic growth in cities with stations on upgraded rail lines. Over the entire period of the speed-up campaign, the per capita GDP growth rate has risen by 3.7percentage points in cities with upgraded stations versus cities with traditional stations. Moreover, positive effects on economic growth have been found to increase in later stages of railway upgrades.

房地产价格调控新政实施效应实证分析——基于京津两地微观数据

为抑制房地产价格过快上涨,房地产价格调控新政(新国五条)和各地细则于2013年4月1日开始执行。本文基于Web Data Mining技术,利用SAS软件获取了新国五条政策执行前一期以及政策执行后三期京津地区170个小区的二手房屋挂牌价格及相关因素数据。根据改进的倍差法(Difference-in-Difference)模型,对以上数据进行分析,得出了政策对于总体房屋价格的差异,不仅如此,我们还对与不同特性二手房屋价格受到的不同政策影响进行了计量分析。得出了结论:北京新国五条新政对于房屋价格整体有正的影响,促进了北京二手房挂牌价格提升,并且对于学区房和地铁通达性较好的二手房挂牌价格有额外的正的影响,而对于满五年住房挂牌价格影响并不显著。并且进一步的提出了政策建议。

Quantifying the effects of stripe rust disease on wheat canopy spectrum based on eliminating non-physiological stresses

The wheat canopy reflectance spectrum is affected by many internal and external factors such as diseases and growth stage. Separating the effects of disease stress on the crop from the observed mixed signals is crucial for increasing the precision of remote sensing monitoring of wheat stripe rust. The canopy spectrum of winter wheat infected by stripe rust was processed with the difference-in-differences(DID) algorithm used in econometrics. The monitoring accuracies of wheat stripe rust before and after processing with the DID algorithm were compared in the presence of various external factors, disease severity, and several simulated satellite sensors. The correlation between the normalized difference vegetation index processed by the DID algorithm(NDVI-DID) and the disease severity level(SL) increased in comparison with the NDVI before processing. The increase in precision in the natural disease area in the field in the presence of large differences in growth stage, growth, planting, and management of the crop was greater than that in the controlled experiment. For low disease levels(SL < 20%), the R2 of the regression of NDVI-DIDon SL was 38.8% higher than that of the NDVI and the root mean square error(RMSE) was reduced by 11.1%. The increase in precision was greater than that for the severe level(SL > 40%).According to the measured hyperspectral data, the spectral reflectance of three satellite sensor levels was simulated. The wide-band NDVI was calculated. Compared with the wide-band NDVI and vegetation indexes(VI) before DID processing, there were increases in the correlation between SL and the various types of VIS-DID, as well as in the correlation between SL and NDVI-DID. It is feasible to apply the DID algorithm to multispectral satellite data and diverse types of VISfor monitoring wheat stripe rust. Our results improve the quantification of independent effects of stripe rust infection on canopy reflectance spectrum,increase the precision of remote sensing monitoring of wheat stripe rust, and provide a reference for remote sensing monitoring of other crop diseases.

Transportation Infrastructure and Productivity Growth:Effects of Railway Speed-Up on Firm's TFP in China

Improvement of transportation infrastructure quality will lead to more sufficient market competition and promote the flow of resources with greater efficiency. This paper considers China's railway speed-up in 2007 as a quasi-natural experiment on China's transportation infrastructure quality improvement. With the initial operation of electric multiple units(EMUs) as the basis of grouping, this research examines the effect of railway speed-up on corporate total factor productivity(TFP) growth by the differencein-differences(DID) method. Overally, the results reveal positive effects both on firms' technological change and efficiency improvement, which lead to the increase of TFP. Based on subsamples divided by different regions and types of enterprises, further analysis indicates that the productivity of exporter, non-state and coastal firms has been mostly affected by the railway speed-up. These conclusions are verified by a placebo test. Besides, firms within "one-hour economic circle" have been shown more sensitive to the effect of railway speed increase.

Impact of the green credit policy on external financing,economic growth and energy consumption of the manufacturing industry

China attempts to achieve energy conservation,emission reduction and environmental protection through the implementation of the green credit policy,but its implementation impact is still controversial.An important content of the green credit policy is to require banking and financial institutions to tighten the credit exposure of industries of‘high pollution and high energy consumption’and industries with overcapacity,so as to use economic leverage to curb their blind expansion and reduce energy consumption by controlling external financing.This paper examined the impact and the lingering effects of the green credit policy on external financing,economic growth and energy consumption in the manufacturing industry,which was most influenced by the green credit policy,from 2003 to 2016 by using the DID method.Furthermore,this paper estimated the dynamic endogenous relationships among external financing,economic growth and energy consumption with two-step system GMM model to investigate the influential path of the green credit policy.The results showed that:the green credit policy had a significant negative impact on the external financing of manufacturing industry,but its negative impact on the economic growth and energy consumption of manufacturing industry was not statistically significant,and the effect of the green credit policy had a dynamic feature of weakening with time.Additionally,in the manufacturing industry,there was a bilateral causal relationship between the energy consumption and economic growth of the control group industry and the processing group industry.There was a bilateral causal relationship between the economic growth and external financing of the control group industries in the manufacturing industry.There was a unilateral causal relationship between the economic growth and external financing of the processing group industries in the manufacturing industry,while the external causality existed between the control group industries and the processing group industries in the manufacturing industry.The causal relationship between the financing and energy consumption was not statistically significant.At present,the transmission path of the green credit policy is that the green credit policy controls external financing,then affects economic growth and ultimately inhibits energy consumption,but the effectiveness of the path is not statistically significant.The conclusion of this paper provides policy reference and scientific basis for the adjustment and improvement of green credit.

Effects of the Northeast China Revitalization Strategy on Regional Economic Growth and Social Development

Measuring the economic and social effects of the Northeast China Revitalization Strategy is critical to addressing regional sustainable development in China. To shed light on this issue, an integrated perspective was adopted that is combined with the difference-in-differences method to measure the effects of the strategy on economic growth and social development in Northeast China. The findings suggest that the strategy has significantly improved regional economic growth and per-capita income by increasing its gross domestic product(GDP) and GDP per capita by 25.70% and 46.00%, respectively. However, the strategy has significantly worsened the regional employment in the secondary industry of the region. In addition, the strategy has not significantly improved regional infrastructural road, education investment or social security, and has had no significant effect on mitigating regional disparity. In addition, the policy effects are highly heterogeneous across cities based on city size and characteristics. Therefore, there is no simple answer regarding whether the Northeast China Revitalization Strategy has reached its original goals from an integrated perspective. The next phase of the strategy should emphasize improving research and development(R&D) and human capital investments based on urban heterogeneity to prevent conservative path-dependency and the lock-in of outdated technologies.