The effect on citation inequality of differences in citation practices at the Web of Sciences subject category level

This paper studies the impact of differences in citation practices at the sub-field, or Web of Science subject category level using the model introduced in Crespo et al. (2012) according to which the number of citations received by an article depends on its underlying scientific influence and the field to which it belongs. We use the same Thomson Reuters dataset of about 4.4 million articles published in 1998-2003 with a fiveyear citation window used in Crespo et al. (2013) to analyze a classification system consisting of 22 broad fields. The main results are the following four. Firstly, as expected, when the classification system goes from 22 broad fields to 219 sub-fields the effect on citation inequality of differences in citation practices increases from approximately 14% at the field level to 18% at the sub-field level. Secondly, we estimate a set of exchange rates (ERs) to express the citation counts of articles in a wide quantile interval into the equivalent counts in the all-sciences case. For example, in the fractional case we find that in 187 out of 219 sub-fields the ERs are reliable in the sense that the coefficient of variation is smaller than or equal to 0.10. ERs are estimated over the [660, 978] interval that, on average, covers about 62% of all citations. Thirdly, in the fractional case the normalization of the raw data using the ERs (or sub-field mean citations) as normalization factors reduces the importance of the differences in citation practices from 18% to 3.8% (3.4%) of overall citation inequality. Fourthly, the results in the fractional case are essentially replicated when we adopt the multiplicative approac

Three essays on applied economics

This thesis focuses on the application of empirical research methods to different economic topics. The first chapter examines production effects of subsidies with different characteristics. The second chapter evaluates the impact of an oldage pension program on the welfare of the recipient’s family members. The third chapter applies an income inequality model to study the influence of differences in citation practices across scientific fields on the overall citation inequality. Chapter 1, “Differential Effects on Output Levels of Binding and non-Binding Subsidies under Capitalization”. Subsidies on outputs or inputs are usually production-promoting by lowering the marginal cost. However, if subsidies are binding, i.e. outputs or inputs are partially subsidized, subsidies don’t affect the output level. If subsidies capitalize into input prices, i.e. subsidies benefit both the recipients and input providers, outputs will be negatively affected. My paper contributes by empirically assessing production effects of subsidies taking into account both bindingness and capitalization. I study cattle payments under the Common Agricultural Policy (CAP) implemented in the European Union (EU). I set up a simple model to analyze production effects of these payments. I also estimate the effects with Spanish farm-level data. CAP 1992 and Agenda 2000 are two policy programs of the CAP. Both are designed to reduce over-production in agriculture. Estimation results suggest that cattle payments have negative impacts on outputs when they are binding under CAP 1992, and positive impacts when they are non-binding under Agenda 2000. Chapter 2, “Reassessing the Differential Impact of Grandmothers and Grandfathers: The Old Age Program in Nepal” (co-authored with Ricardo Mora). We study the effects on infant mortality of the introduction in 1995 of a non-contributory universal pension scheme in Nepal known as the Old age Allowance Program. We use cross-sectional data from the 1996 and 2001 Nepal Demographic and Health Surveys. Following a standard diff-in-diffs approach, we find positive and significant effects on survival rates for the presence in the same household of a female beneficiary while negative and sometimes significant effects for the presence of a male beneficiary. When we conduct pre-treatment common trend tests, we find that we cannot reject it for the case of the female beneficiaries but we strongly reject it for the case of male beneficiaries. Following Mora and Reggio (2012), we then propose a more flexible model and identification strategy and find that there are no differences in the female and the male beneficiary effects. We interpret these results as suggestive that cross-sectional analysis may bias downwards the estimates of the effect of grandfathers because of gender differences in endogenous household formation. Chapter 3 is a combination of two closely related papers, namely “The Measurement of the Effect on Citation Inequality of Differences in Citation Practices across Scientific Fields” (co-authored with Juan A. Crespo and Javier Ruiz-Castillo, published in PLoS ONE 8(3): e58727 (2013)), and “The Effect on Citation Inequality of Differences in Citation Practices at the Web of Science Subject Category Level” (co-authored with Juan A. Crespoa, Neus Herranz and Javier Ruiz-Castillo, published in Journal of the American Society for Information Science and Technology, 65:1244-1256, (June 2014)). We introduce a novel method for measuring which part of overall citation inequality can be attributed to differences in citation practices across scientific fields. In addition, we implement an empirical strategy for making meaningful comparisons between the numbers of citations received by articles in different scientific fields. Using a dataset of 4.4 million articles published in 1998-2003 with a five-year citation window, we find that differences in citation practices between the 22 fields account for about 14% of overall citation inequality. When the classification system goes from 22 fields to 219 sub-fields, the effect on citation inequality increases to about 18%. For comparisons of citation counts across fields, we provide a set of exchange rates (ERs) to express citations in any field into citations in the all-fields case. When the raw citation data are normalized with our ERs, the effect of differences in citation practices is reduced to around 2% of overall citation inequality in the case of 22 fields. In the case of 219 sub-fields with the fractional strategy, the normalization of the raw data using the ERs (or sub-field mean citations) as normalization factors reduces the effect to 3.8% (3.4%) of overall citation inequality. The results with the fractional strategy are essentially replicated when we adopt a multiplicative approach.Programa Oficial de Doctorado en EconomíaPresidente: Joan Crespo Fernández; Secretario: Jesús María Carro Prieto; Vocal: Fernando Martín Aragón Sánche

A systematic empirical comparison of different approaches for normalizing citation impact indicators

We address the question how citation-based bibliometric indicators can best be normalized to ensure fair comparisons between publications from different scientific fields and different years. In a systematic large-scale empirical analysis, we compare a traditional normalization approach based on a field classification system with three source normalization approaches. We pay special attention to the selection of the publications included in the analysis. Publications in national scientific journals, popular scientific magazines, and trade magazines are not included. Unlike earlier studies, we use algorithmically constructed classification systems to evaluate the different normalization approaches. Our analysis shows that a source normalization approach based on the recently introduced idea of fractional citation counting does not perform well. Two other source normalization approaches generally outperform the classification-system-based normalization approach that we study. Our analysis therefore offers considerable support for the use of source-normalized bibliometric indicators

Within- and between-department variability in individual productivity. The case of Economics

There are two types of research units whose performance is usually investigated in one or several scientific fields: individuals (or publications), or larger units such as universities or entire countries. In contrast, the information about the university departments (or research institutes) is not easy to come by. This is important because, in the social sciences, university departments are the governance units where the demand for and the supply of researchers determine an equilibrium allocation of scholars to institutions. This paper uses a unique dataset consisting of all individuals working in 2007 in the top 81 Economics departments in the world according to the Econphd university ranking

Quantitative evaluation of alternative field normalization procedures

ide differences in publication and citation practices makes impossible the direct comparison of raw citation counts across scientific disciplines. Recent research has studied new and traditional normalization procedures aimed at suppressing as much as possible these disproportions in citation numbers among scientific domains. Using the recently introduced IDCP (Inequality due to Differences in Citation Practices) method, this paper rigorously tests the performance of six cited-side normalization procedures based on the Thomson Reuters classification system consisting of 172 subfields. We use six yearly datasets from 1980 to 2004, with widely varying citation windows from the publication year to May 2011. The main findings are the following three. Firstly, as observed in previous research, within each year the shapes of sub-field citation distributions are strikingly similar. This paves the way for several normalization procedures to perform reasonably well in reducing the effect on citation inequality of differences in citation practices. Secondly, independently of the year of publication and the length of the citation window, the effect of such differences represents about 13% of total citation inequality. Thirdly, a recently introduced two-parameter normalization scheme outperforms the other normalization procedures over the entire period, reducing citation disproportions to a level very close to the minimum achievable given the data and the classification system. However, the traditional procedure of using sub-field mean citations as normalization factors yields also good results.Ruiz-Castillo acknowledges financial help from the Spanish MEC through grant ECO2011-2976

Within and across department variability in individual productivity : the case of economics

University departments (or research institutes) are the governance units in any scientific field where the demand for and the supply of researchers interact. As a first step towards a formal model of this process, this paper investigates the characteristics of productivity distributions of a population of 2,530 individuals with at least one publication who were working in 81 world top Economics departments in 2007. Individual productivity is measured in two ways: as the number of publications until 2007, and as a quality index that weights differently the articles published in four journal equivalent classes. The academic age of individuals, measured as the number of years since obtaining the PhD until 2007, is used to measure productivity per year. Independently of the two productivity measures, and both before and after age normalization, the main findings of the paper are the following five. Firstly, individuals within each department have very different productivities. Secondly, there is not a single pattern of productivity inequality and skewness at the department level. On the contrary, productivity distributions are very different across departments. Thirdly, the effect on overall productivity inequality of differences in productivity distributions across departments is greater than the analogous effect in other contexts. Fourthly, to a large extent, this effect on overall productivity inequality is accounted for by scale factors well captured by departments’ mean productivities. Fifthly, this high degree of departmental heterogeneity is found to be compatible with greater homogeneity across the members of a partition of the sample into seven countries and a residual category.Ruiz-Castillo acknowledges financial support from the Spanish MEC through grant SEJ2007-6743

The comparison of classification-system-based normalization procedures with source normalization alternatives in Waltman and Van Eck (2013)

Waltman & Van Eck, in press, contains a systematic large-scale empirical comparison of classification-system-based versus source normalization procedures. A source-normalization procedure SNCS performs better than a normalization procedure based on the system where publications are classified into fields according to the journal subject categories in the Web of Science bibliographic database. Using the same data and the same methods, in this note we confront SNCS with the best possible procedure among those based on three available algorithmic classification systems. Our conclusions raise some doubts concerning the idea that source normalization procedures are ready to supplant their classification-system-based alternatives

Differences in citation impact across countries

Using a large dataset, indexed by Thomson Reuters, consisting of 4.4 million articles published in 1998-2003 with a five-year citation window for each year, this paper studies country citation distributions in a partition of the world into 36 countries and two geographical areas in the all-sciences case and eight broad scientific fields. The key findings are the following two. Firstly, the shape of country citation distributions is highly skewed and very similar to each other across all fields. Secondly, differences in country citation distributions appear to have a strong scale factor component. The implication is that, in spite of the skewness of citation distributions, international comparisons of citation impact in terms of country mean citations capture well such scale factors. The empirical scenario described in the paper helps understanding why, in each field and the all-sciences case, the country rankings according to (i) mean citations and (ii) the percentage of articles in each country belonging to the set formed by the 10% of the more highly cited papers are so similar to each other.Albarrán acknowledges additional financial support from the Spanish MEC through grants ECO2009-11165 and ECO2011-29751, and Ruiz-Castillo through grant SEJ2007-67436