The Distribution of the Asymptotic Number of Citations to Sets of Publications by a Researcher or From an Academic Department Are Consistent With a Discrete Lognormal Model

How to quantify the impact of a researcher's or an institution's body of work is a matter of increasing importance to scientists, funding agencies, and hiring committees. The use of bibliometric indicators, such as the h-index or the Journal Impact Factor, have become widespread despite their known limitations. We argue that most existing bibliometric indicators are inconsistent, biased, and, worst of all, susceptible to manipulation. Here, we pursue a principled approach to the development of an indicator to quantify the scientific impact of both individual researchers and research institutions grounded on the functional form of the distribution of the asymptotic number of citations. We validate our approach using the publication records of 1,283 researchers from seven scientific and engineering disciplines and the chemistry departments at the 106 U.S. research institutions classified as "very high research activity". Our approach has three distinct advantages. First, it accurately captures the overall scientific impact of researchers at all career stages, as measured by asymptotic citation counts. Second, unlike other measures, our indicator is resistant to manipulation and rewards publication quality over quantity. Third, our approach captures the time-evolution of the scientific impact of research institutions.Comment: 20 pages, 11 figures, 3 table

Minimum impact and immediacy of citations to physics open archives of arXiv.org: Science Citation Index based reports

The present work has calculated the minimum Open Archive Impact Factors and Open Archive Immediacy Index for the Physics Classes of arXiv.org as calculated for traditional journals in Journal Citation Reports of the Institute of Scientific Information using Science Citation Index without the citation by the classes itself. The calculated Impact Factors reveal that High-Energy Physics classes of arXiv.org (‘hep-th’, ‘hep-lat’, ‘hep-ex’, and ‘hep-ph’) have made more impact on the scientific community than any other classes except ‘nucl-ex’. The Impact Factors for the year 2003 are: ‘hep-th’ (0.999), ‘nucl-ex’ (0.806), ‘hep-lat’ (0.766), ‘hep-ex’ (0.73), ‘hep-ph’ (0.719), ‘nucl-th’ (0.338), ‘quant-ph’ (0.334), ‘cond-mat’ (0.313), ‘astro-ph’ (0.195), ‘math-ph’ (0.162), ‘physics’ (0.061), and ‘gr-qc’ (0.002). If the period for getting the citations to the open archive classes is considered one year as against two years for journal articles, the rank of the classes is the same. The immediacy of citing the Open Archives is also high for the High-Energy Physics classes. The Immediacy Indexes for the year 2003 are: ‘hep-ex’ (0.619), ‘hep-th’ (0.454), ‘hep-ph’ (0.44), ‘hep-lat’ (0.263), ‘nucl-ex’ (0.238), ‘quant-ph’ (0.202), ‘nucl-th’ (0.185), ‘cond-mat’ (0.168), ‘astro-ph’ (0.094), ‘math-ph’ (0.075), ‘physics’ (0.03), and ‘gr-qc’ (0.002). The impact is definitely much higher than what is concluded from the calculated factors because self-citations are not reckoned in the study. Use of web-tools like ‘Citebase’, ‘Citeseer’ etc. may strengthen the above argument

The Possible Role of Resource Requirements and Academic Career-Choice Risk on Gender Differences in Publication Rate and Impact

Many studies demonstrate that there is still a significant gender bias, especially at higher career levels, in many areas including science, technology, engineering, and mathematics (STEM). We investigated field-dependent, gender-specific effects of the selective pressures individuals experience as they pursue a career in academia within seven STEM disciplines. We built a unique database that comprises 437,787 publications authored by 4,292 faculty members at top United States research universities. Our analyses reveal that gender differences in publication rate and impact are discipline-specific. Our results also support two hypotheses. First, the widely-reported lower publication rates of female faculty are correlated with the amount of research resources typically needed in the discipline considered, and thus may be explained by the lower level of institutional support historically received by females. Second, in disciplines where pursuing an academic position incurs greater career risk, female faculty tend to have a greater fraction of higher impact publications than males. Our findings have significant, field-specific, policy implications for achieving diversity at the faculty level within the STEM disciplines.Comment: 9 figures and 3 table

Impact Factor: outdated artefact or stepping-stone to journal certification?

A review of Garfield's journal impact factor and its specific implementation as the Thomson Reuters Impact Factor reveals several weaknesses in this commonly-used indicator of journal standing. Key limitations include the mismatch between citing and cited documents, the deceptive display of three decimals that belies the real precision, and the absence of confidence intervals. These are minor issues that are easily amended and should be corrected, but more substantive improvements are needed. There are indications that the scientific community seeks and needs better certification of journal procedures to improve the quality of published science. Comprehensive certification of editorial and review procedures could help ensure adequate procedures to detect duplicate and fraudulent submissions.Comment: 25 pages, 12 figures, 6 table

The influence of self-citation corrections on Egghe's g index

The g index was introduced by Leo Egghe as an improvement of Hirsch's index h for measuring the overall citation record of a set of articles. It better takes into account the highly skewed frequency distribution of citations than the h index. I propose to sharpen this g index by excluding the self-citations. I have worked out nine practical cases in physics and compare the h and g values with and without self-citations. As expected, the g index characterizes the data set better than the h index. The influence of the self-citations appears to be more significant for the g index than for the h index.Comment: 9 pages, 2 figures, submitted to Scientometric

A case study of the Hirsch index for 26 non-prominent physicists

The h index was introduced by Hirsch to quantify an individual's scientific research output. It has been widely used in different fields to show the relevance of the research work of prominent scientists. I have worked out 26 practical cases of physicists which are not so prominent. Therefore this case study should be more relevant to discuss various features of the Hirsch index which are interesting or disturbing or both for the more average situation. In particular, I investigate quantitatively some pitfalls in the evaluation and the influence of self-citations.Comment: 13 pages, 3 figures, updated after extensive language editing, no other changes to first versio

Environmental and Ecological Economics: A Citation Analysis

This study looks at two distinct questions: What have been the most influential journal articles in environmental economics over the ten year period 1994-2003? and, how much overlap is there between the fields of environmental and ecological economics? We examine the references in all articles published in JEEM and Ecological Economics (EE) over this period. For each of these two fields, a list of the top articles and top journals cited by articles published in JEEM and EE is presented. We also present some results based on our study of the ISI Journal Citation Reports. We find that there is a significant overlap between the two fields at the journal level - the two journals cite similar journals. There is a correlation of 0.34 between the number of citations received by the journals that are most cited and the correlation is even higher if journal self-citation is excluded. The main differences are that ecological economics tends to cite (but not be cited by) general natural science journals more often than environmental economics does, environmental economics cites more heavily from journals rather than other publications, and citations in environmental economics are more concentrated on particular journals and individual publications. However, there is much less similarity at the level of individual articles. Non-market valuation articles dominate the most cited articles in JEEM while green accounting, sustainability, and environmental Kuznets curve are all prominent topics in EE.

Studying the Emerging Global Brain: Analyzing and Visualizing the Impact of Co-Authorship Teams

This paper introduces a suite of approaches and measures to study the impact of co-authorship teams based on the number of publications and their citations on a local and global scale. In particular, we present a novel weighted graph representation that encodes coupled author-paper networks as a weighted co-authorship graph. This weighted graph representation is applied to a dataset that captures the emergence of a new field of science and comprises 614 papers published by 1,036 unique authors between 1974 and 2004. In order to characterize the properties and evolution of this field we first use four different measures of centrality to identify the impact of authors. A global statistical analysis is performed to characterize the distribution of paper production and paper citations and its correlation with the co-authorship team size. The size of co-authorship clusters over time is examined. Finally, a novel local, author-centered measure based on entropy is applied to determine the global evolution of the field and the identification of the contribution of a single author's impact across all of its co-authorship relations. A visualization of the growth of the weighted co-author network and the results obtained from the statistical analysis indicate a drift towards a more cooperative, global collaboration process as the main drive in the production of scientific knowledge.Comment: 13 pages, 9 figure