Pub Date : 2018-02-19DOI: 10.1920/WP.IFS.2018.W1805
Hamish Low, C. Meghir, Luigi Pistaferri, Alessandra Voena
The 1996 PRWORA reform introduced time limits on the receipt of welfare in the United States. We use variation by state and across demographic groups to provide reduced form evidence showing that such limits led to a fall in welfare claims (partly due to "banking" benefits for future use), a rise in employment, and a decline in divorce rates. We then specify and estimate a life-cycle model of marriage, labor supply and divorce under limited commitment to better understand the mechanisms behind these behavioral responses, carry out counterfactual analysis with longer run impacts and evaluate the welfare effects of the program. Based on the model, which reproduces the reduced form estimates, we show that among low educated women, instead of relying on TANF, single mothers work more, more mothers remain married, some move to relying only on food stamps and, in ex-ante welfare terms, women are worse off.
{"title":"Marriage, labour supply and the dynamics of the social safety net","authors":"Hamish Low, C. Meghir, Luigi Pistaferri, Alessandra Voena","doi":"10.1920/WP.IFS.2018.W1805","DOIUrl":"https://doi.org/10.1920/WP.IFS.2018.W1805","url":null,"abstract":"The 1996 PRWORA reform introduced time limits on the receipt of welfare in the United States. We use variation by state and across demographic groups to provide reduced form evidence showing that such limits led to a fall in welfare claims (partly due to \"banking\" benefits for future use), a rise in employment, and a decline in divorce rates. We then specify and estimate a life-cycle model of marriage, labor supply and divorce under limited commitment to better understand the mechanisms behind these behavioral responses, carry out counterfactual analysis with longer run impacts and evaluate the welfare effects of the program. Based on the model, which reproduces the reduced form estimates, we show that among low educated women, instead of relying on TANF, single mothers work more, more mothers remain married, some move to relying only on food stamps and, in ex-ante welfare terms, women are worse off.","PeriodicalId":18934,"journal":{"name":"National Bureau of Economic Research","volume":"38 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2018-02-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80085927","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
One source of uncertainty in the patent system relates to the difficulty in identifying products that are protected with a patent. This paper studies the adoption by U.S. patentees of “virtual patent marking,” namely the online provision of constructive notice to the public that an article is patented. It proposes a simple model of the decision to adopt patent marking and empirically examines factors that affect adoption. Data suggest that about 12 percent of patent holders overall provide virtual marking information (and perhaps about 25 percent of commercially active assignees). Econometric analysis suggests that the most discriminant factor of the adoption of virtual marking is the size of the patent portfolio. The likelihood of adoption increases with portfolio size, consistent with evidence that firms with a larger patent portfolio are more likely to be infringed.
{"title":"Notice failure revisited: Evidence on the use of virtual patent marking","authors":"Gaétan de Rassenfosse","doi":"10.3386/W24288","DOIUrl":"https://doi.org/10.3386/W24288","url":null,"abstract":"One source of uncertainty in the patent system relates to the difficulty in identifying products that are protected with a patent. This paper studies the adoption by U.S. patentees of “virtual patent marking,” namely the online provision of constructive notice to the public that an article is patented. It proposes a simple model of the decision to adopt patent marking and empirically examines factors that affect adoption. Data suggest that about 12 percent of patent holders overall provide virtual marking information (and perhaps about 25 percent of commercially active assignees). Econometric analysis suggests that the most discriminant factor of the adoption of virtual marking is the size of the patent portfolio. The likelihood of adoption increases with portfolio size, consistent with evidence that firms with a larger patent portfolio are more likely to be infringed.","PeriodicalId":18934,"journal":{"name":"National Bureau of Economic Research","volume":"52 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2018-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77061606","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Contrary to common perception, many fixed-income investors have not suffered unusually low real interest rates in and after the Great Recession of 2008. This is because taxable investors must first pay taxes on nominal interest returns, before inflation further reduces their earned real interest rates. To obtain the same real after-tax yield, investors need more than one-to-one compensation for inflation. As a result, long-term Treasury bonds have been no less attractive for taxable investors in 2016 (with a 1.0% post-tax real yield) than they were in 2006 (0.5%), 1976 (–1.7%), 1966 (0.9%), and 1956 (0.8%), although they have been less attractive than they were in 1996 (2.4%) and 1986 (2.9%). Short-term Treasury bond yields have been on the low side but have also not been particularly unusual.
{"title":"Are Interest Rates Really Low","authors":"D. Feenberg, Clinton Tepper, I. Welch","doi":"10.3386/W24258","DOIUrl":"https://doi.org/10.3386/W24258","url":null,"abstract":"Contrary to common perception, many fixed-income investors have not suffered unusually low real interest rates in and after the Great Recession of 2008. This is because taxable investors must first pay taxes on nominal interest returns, before inflation further reduces their earned real interest rates. To obtain the same real after-tax yield, investors need more than one-to-one compensation for inflation. As a result, long-term Treasury bonds have been no less attractive for taxable investors in 2016 (with a 1.0% post-tax real yield) than they were in 2006 (0.5%), 1976 (–1.7%), 1966 (0.9%), and 1956 (0.8%), although they have been less attractive than they were in 1996 (2.4%) and 1986 (2.9%). Short-term Treasury bond yields have been on the low side but have also not been particularly unusual.","PeriodicalId":18934,"journal":{"name":"National Bureau of Economic Research","volume":"48 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2018-01-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"89305133","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper provides an equilibrium theory of liquidity traps and the real effects of money. Money provides a safe store of value that prevents interest rates from falling enough during downturns, and the economy enters a persistent slump with depressed investment. This is an equilibrium outcome—prices are flexible, markets clear, and inflation is on target—but it’s not efficient. Investment is too high during booms and too low during liquidity traps. Although money has large real effects, monetary policy is ineffective—the zero lower bound is not binding, money is superneutral, and Ricardian equivalence holds. The optimal allocation requires the Friedman rule and a tax/subsidy on capital.
{"title":"A Neoclassical Theory of Liquidity Traps","authors":"S. D. Tella","doi":"10.3386/W24205","DOIUrl":"https://doi.org/10.3386/W24205","url":null,"abstract":"This paper provides an equilibrium theory of liquidity traps and the real effects of money. Money provides a safe store of value that prevents interest rates from falling enough during downturns, and the economy enters a persistent slump with depressed investment. This is an equilibrium outcome—prices are flexible, markets clear, and inflation is on target—but it’s not efficient. Investment is too high during booms and too low during liquidity traps. Although money has large real effects, monetary policy is ineffective—the zero lower bound is not binding, money is superneutral, and Ricardian equivalence holds. The optimal allocation requires the Friedman rule and a tax/subsidy on capital.","PeriodicalId":18934,"journal":{"name":"National Bureau of Economic Research","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2018-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"74225570","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
This paper sheds new light on general equilibrium responses to major education reforms, focusing on a sorting mechanism likely to operate whenever a reform improves public school quality significantly. It does so in the context of California’s statewide class size reduction program of the late-1990s, and makes two main contributions. First, using a transparent differencing strategy that exploits the grade-specific roll-out of the reform, we show evidence of general equilibrium sorting effects: Improvements in public school quality caused marked reductions in local private school shares, consequent changes in public school demographics, and significant increases in local house prices – the latter indicative of the reform’s full impact. Second, using a generalization of the differencing approach, we provide credible estimates of the direct and indirect impacts of the reform on a common scale. These reveal a large pure class size effect of 0.11Iƒ (in terms of mathematics scores), and an even larger indirect effect of 0.16Iƒ via induced changes in school demographics. Further, we show that both effects persist positively, giving rise to an overall policy impact estimated to be 0.4Iƒ higher after four years of treatment (relative to none). The analysis draws attention, more broadly, to conditions under which the indirect sorting effects of major reforms are likely to be first order.
本文为重大教育改革的一般均衡反应提供了新的视角，重点关注了每当改革显著提高公立学校质量时可能运行的分类机制。它是在20世纪90年代末加州全州范围内的班级规模缩减计划的背景下进行的，并做出了两个主要贡献。首先，我们采用透明的差异策略，利用改革的具体年级展开，展示了一般均衡分类效应的证据:公立学校质量的提高导致当地私立学校份额的显著减少，随之而来的是公立学校人口结构的变化，以及当地房价的显著上涨——后者表明了改革的全面影响。其次，利用差分法的一般化方法，我们在一个共同的尺度上对改革的直接和间接影响提供了可信的估计。这些研究揭示了一个巨大的纯班级规模效应(以数学成绩计算)，达到0.11 if - f，而通过学校人口统计数据的变化，间接影响甚至更大，达到0.16 if - f。此外，我们表明，这两种效应都是积极的，在治疗四年后，总体政策影响估计高出0.4 if(相对于没有治疗)。这一分析在更广泛的范围内引起了人们的注意，即在哪些条件下，重大改革的间接排序效应可能是首要的。
{"title":"Education Reform in General Equilibrium: Evidence from California's Class Size Reduction","authors":"Michael Gilraine, Hugh Macartney, R. Mcmillan","doi":"10.3386/W24191","DOIUrl":"https://doi.org/10.3386/W24191","url":null,"abstract":"This paper sheds new light on general equilibrium responses to major education reforms, focusing on a sorting mechanism likely to operate whenever a reform improves public school quality significantly. It does so in the context of California’s statewide class size reduction program of the late-1990s, and makes two main contributions. First, using a transparent differencing strategy that exploits the grade-specific roll-out of the reform, we show evidence of general equilibrium sorting effects: Improvements in public school quality caused marked reductions in local private school shares, consequent changes in public school demographics, and significant increases in local house prices – the latter indicative of the reform’s full impact. Second, using a generalization of the differencing approach, we provide credible estimates of the direct and indirect impacts of the reform on a common scale. These reveal a large pure class size effect of 0.11Iƒ (in terms of mathematics scores), and an even larger indirect effect of 0.16Iƒ via induced changes in school demographics. Further, we show that both effects persist positively, giving rise to an overall policy impact estimated to be 0.4Iƒ higher after four years of treatment (relative to none). The analysis draws attention, more broadly, to conditions under which the indirect sorting effects of major reforms are likely to be first order.","PeriodicalId":18934,"journal":{"name":"National Bureau of Economic Research","volume":"25 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2018-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"90237618","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Mila Getmansky, R. Jagannathan, L. Pelizzon, E. Schaumburg, Darya Yuferova
We study the role of various trader types in providing liquidity in spot and futures markets based on complete order-book and transactions data as well as cross-market trader identifiers from the National Stock Exchange of India for a single large stock. During normal times, short-term traders who carry little inventory overnight are the primary intermediaries in both spot and futures markets, and changes in futures prices Granger-cause changes in spot prices. However, during two days of fast crashes, Granger-causality ran both ways. Both crashes were due to large-scale selling by foreign institutional investors in the spot market. Buying by short-term traders and cross-market traders was insufficient to stop the crashes. Mutual funds, patient traders with better trade-execution quality who were initially slow to move in, eventually bought sufficient quantities leading to price recovery in both markets. Our findings suggest that market stability requires the presence of well-capitalized standby liquidity providers.
{"title":"Stock price crashes: Role of slow-moving capital","authors":"Mila Getmansky, R. Jagannathan, L. Pelizzon, E. Schaumburg, Darya Yuferova","doi":"10.3386/w24098","DOIUrl":"https://doi.org/10.3386/w24098","url":null,"abstract":"We study the role of various trader types in providing liquidity in spot and futures markets based on complete order-book and transactions data as well as cross-market trader identifiers from the National Stock Exchange of India for a single large stock. During normal times, short-term traders who carry little inventory overnight are the primary intermediaries in both spot and futures markets, and changes in futures prices Granger-cause changes in spot prices. However, during two days of fast crashes, Granger-causality ran both ways. Both crashes were due to large-scale selling by foreign institutional investors in the spot market. Buying by short-term traders and cross-market traders was insufficient to stop the crashes. Mutual funds, patient traders with better trade-execution quality who were initially slow to move in, eventually bought sufficient quantities leading to price recovery in both markets. Our findings suggest that market stability requires the presence of well-capitalized standby liquidity providers.","PeriodicalId":18934,"journal":{"name":"National Bureau of Economic Research","volume":"79 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-12-07","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"81494835","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
International trade is primarily conducted by large, multiproduct firms (MPFs) that pay above average wages and exhibit high productivity. In this paper we show that if firms can invest in management technologies for identifying worker skill then they will enjoy a form of market power in the labor market that artificially lowers their labor costs. This market failure results in excessive consumption of resources by large, productive exporting firms relative to the social optimum. Trade liberalization then has an ambiguous effect on aggregate welfare: lower trade costs increase access to foreign goods but also exacerbates the labor market distortion as resources are transferred to large firms. The model highlights the need to know why firms "excel" before drawing welfare conclusions regarding cross firm reallocations of resources.
{"title":"Too Much of a Good Thing? Exporters, Multiproduct Firms and Labor Market Imperfections","authors":"C. Eckel, S. Yeaple","doi":"10.3386/w23834","DOIUrl":"https://doi.org/10.3386/w23834","url":null,"abstract":"International trade is primarily conducted by large, multiproduct firms (MPFs) that pay above average wages and exhibit high productivity. In this paper we show that if firms can invest in management technologies for identifying worker skill then they will enjoy a form of market power in the labor market that artificially lowers their labor costs. This market failure results in excessive consumption of resources by large, productive exporting firms relative to the social optimum. Trade liberalization then has an ambiguous effect on aggregate welfare: lower trade costs increase access to foreign goods but also exacerbates the labor market distortion as resources are transferred to large firms. The model highlights the need to know why firms \"excel\" before drawing welfare conclusions regarding cross firm reallocations of resources.","PeriodicalId":18934,"journal":{"name":"National Bureau of Economic Research","volume":"15 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"84340816","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We study the consequences of dynamic complementarities in the production of child human capital for the relationship between risk and schooling investment in a low income setting. In contrast to previous literature, we explore the ex ante response of schooling to risk. We develop a model that incorporates, dynamic complementarity in the education production function, ex-post labor market responses by mothers to income shocks, and substitutability between maternal and child work in the household. We test the model using data from rural India, focusing particularly on the schooling of girls. We find that risk substantially reduces the probability that girls attend school. We then simulate the effects of an implicit social insurance program, modeled after the National Rural Employment Guarantee Scheme (NREGS). Our results suggest that the risk-reducing effect of the NREGS may offset adverse effects on child education that were evident during the NREGS phase-in due to rising wages.
{"title":"Consumption Risk and Human Capital Accumulation in India","authors":"A. Foster, Esther Gehrke","doi":"10.3386/w24041","DOIUrl":"https://doi.org/10.3386/w24041","url":null,"abstract":"We study the consequences of dynamic complementarities in the production of child human capital for the relationship between risk and schooling investment in a low income setting. In contrast to previous literature, we explore the ex ante response of schooling to risk. We develop a model that incorporates, dynamic complementarity in the education production function, ex-post labor market responses by mothers to income shocks, and substitutability between maternal and child work in the household. We test the model using data from rural India, focusing particularly on the schooling of girls. We find that risk substantially reduces the probability that girls attend school. We then simulate the effects of an implicit social insurance program, modeled after the National Rural Employment Guarantee Scheme (NREGS). Our results suggest that the risk-reducing effect of the NREGS may offset adverse effects on child education that were evident during the NREGS phase-in due to rising wages.","PeriodicalId":18934,"journal":{"name":"National Bureau of Economic Research","volume":"191 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-11-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"77755508","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Krishnamurthy, S. Nagel, Annette Vissing-Jorgensen
We evaluate the effects of three ECB policies (the Securities Markets Programme, the Outright Monetary Transactions, and the Long-Term Refinancing Operations) on government bond yields. We use a novel Kalman-filter augmented event-study approach and yields on euro-denominated sovereign bonds, dollar-denominated sovereign bonds, corporate bonds, and corporate CDS rates to understand the channels through which policies reduced sovereign bond yields. On average across Italy, Spain and Portugal, considering both the Securities Markets Programme and the Outright Monetary Transactions, yields fall considerably. Decomposing this fall, default risk accounts for 37% of the reduction in yields, reduced redenomination risk for 13%, and reduced market segmentation effects for 50%. Stock price increases in distressed and core countries suggest that these policies also had beneficial macro-spillovers.
{"title":"ECB Policies Involving Government Bond Purchases: Impact and Channels","authors":"A. Krishnamurthy, S. Nagel, Annette Vissing-Jorgensen","doi":"10.3386/W23985","DOIUrl":"https://doi.org/10.3386/W23985","url":null,"abstract":"We evaluate the effects of three ECB policies (the Securities Markets Programme, the Outright Monetary Transactions, and the Long-Term Refinancing Operations) on government bond yields. We use a novel Kalman-filter augmented event-study approach and yields on euro-denominated sovereign bonds, dollar-denominated sovereign bonds, corporate bonds, and corporate CDS rates to understand the channels through which policies reduced sovereign bond yields. On average across Italy, Spain and Portugal, considering both the Securities Markets Programme and the Outright Monetary Transactions, yields fall considerably. Decomposing this fall, default risk accounts for 37% of the reduction in yields, reduced redenomination risk for 13%, and reduced market segmentation effects for 50%. Stock price increases in distressed and core countries suggest that these policies also had beneficial macro-spillovers.","PeriodicalId":18934,"journal":{"name":"National Bureau of Economic Research","volume":"36 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-11-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78676066","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The advent of hydraulic fracturing lead to a dramatic increase in US oil production. Due to regulatory, shipping and processing constraints, this sudden surge in domestic drilling caused an unprecedented divergence in crude acquisition costs across US refineries. We take advantage of this exogenous shock to input costs to study the nature of competition and the incidence of cost changes in this important industry. We begin by estimating the extent to which US refining’s divergence from global crude markets was passed on to consumers. Using rich microdata, we are able to decompose the effects of firm-specific, market-specific and industry-wide cost shocks on refined product prices. We show that this distinction has important economic and econometric significance, and discuss the implications for prospective policy which would put a price on carbon emissions. The implications of these results for perennial questions about competition in the refining industry are also discussed.
{"title":"Pass-Through of Input Cost Shocks Under Imperfect Competition: Evidence from the U.S. Fracking Boom","authors":"E. Muehlegger, R. Sweeney","doi":"10.3386/W24025","DOIUrl":"https://doi.org/10.3386/W24025","url":null,"abstract":"The advent of hydraulic fracturing lead to a dramatic increase in US oil production. Due to regulatory, shipping and processing constraints, this sudden surge in domestic drilling caused an unprecedented divergence in crude acquisition costs across US refineries. We take advantage of this exogenous shock to input costs to study the nature of competition and the incidence of cost changes in this important industry. We begin by estimating the extent to which US refining’s divergence from global crude markets was passed on to consumers. Using rich microdata, we are able to decompose the effects of firm-specific, market-specific and industry-wide cost shocks on refined product prices. We show that this distinction has important economic and econometric significance, and discuss the implications for prospective policy which would put a price on carbon emissions. The implications of these results for perennial questions about competition in the refining industry are also discussed.","PeriodicalId":18934,"journal":{"name":"National Bureau of Economic Research","volume":"70 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2017-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"86298565","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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