The influence of author self-citations on bibliometric macro indicators

In a recent paper the authors have studied the role of author self-citations within the process of documented scientific communication. Two important regularities such as the relative fast ageing of self-citations with respect to foreign citations and the “square-root law” characterising the conditional expectation of self-citations for given number of foreign citation have been found studying the phenomenon of author self-citations at the macro level. The goal of the present paper is to study the effect of author self-citations on macro indicators. The analysis of citation based indicators for 15 fields in the sciences, social sciences and humanities substantiates that at this level of aggregation there is no need for any revision of national indicators and the underlying journal citation measures in the context of excluding self-citations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Does co-authorship inflate the share of self-citations?

In recent papers, the authors have studied basic regularities of author self-citations. The regularities are related to the ageing, to the relation between self-citations and foreign citations and to the interdependence of self-citations with other bibliometric indicators. The effect of multi-authorship on citation impact has been shown in other bibliometric studies, for instance, by Persson et al. (2004). The question arises whether those regularities imply any relation between number of co-authors and the extent of author self-citations. The results of the present paper confirm the common notion of such effects only in part. The authors show that at the macro level multi-authorship does not result in any exaggerate extent of self-citations. This revised version was published online in June 2006 with corrections to the Cover Date.     

A bibliometric approach to the role of author self-citations in scientific communication

The present paper analyses the role of author self-citations aiming at finding basic regularities of self-citations within the process of documented scientific communication and thus laying the methodological groundwork for a possible critical view at self-citation patterns in empirical studies at any level of aggregation. The study consists of three parts; the first part of the study is concerned with the comparative analysis of the ageing of self-citations and of non-self citations, in the second part the possible interdependence between self-citations and foreign citations is analysed and in the third part the interrelation of the share of self-citations in all citations with other citation-based indicators is studied. The outcomes of this study are two-fold; first, the results characterise author self-citations - at least at the macro level - as an organic part of the citation process obeying rules that can be measured and described with the help of mathematical models. Second, these rules can be used in evaluative micro and meso analyses to identify significant deviations from the reference standards.     

A concise review on the role of author self-citations in information science, bibliometrics and science policy

Summary  The objective of the present study is twofold: (1) to show the aims and means of quantitative interpretation of bibliographic features in bibliometrics and their re-interpretation in research policy, and (2) to summarise the state-of-art in self-citation research. The authors describe three approaches to the role of author self-citations and possible conflicts arising from the different perspectives. From the bibliometric viewpoint we can conclude that that there is no reason for condemning self-citations in general or for removing them from macro or meso statistics; supplementary indicators based on self-citations are, nonetheless, useful to understand communication patterns.     

Preface

Summary  The objective of the present study is twofold: (1) to show the aims and means of quantitative interpretation of bibliographic features in bibliometrics and their re-interpretation in research policy, and (2) to summarise the state-of-art in self-citation research. The authors describe three approaches to the role of author self-citations and possible conflicts arising from the different perspectives. From the bibliometric viewpoint we can conclude that that there is no reason for condemning self-citations in general or for removing them from macro or meso statistics; supplementary indicators based on self-citations are, nonetheless, useful to understand communication patterns.     

The weight of author self-citations. A fractional approach to self-citation counting

The discussion about how to treat author self-citations driven by policy application and quality measurement intensified in the last years. The definition introduced by Snyder and Bonzi has — in lack of any reasonable alternative — been used in bibliometric practice for science policy purposes. This method, however, does not take into account the weight of self-citing authors among coauthors of both the cited and citing papers. The objective of the present paper is to quantify the weight of self-citations with respect to co-authorship. The analysis is conducted at two levels: at the macro level, namely, for fifteen subject fields and the most active forty countries, and at the meso level, for a set of selected research institutions.     

Research performance indicators for university departments: A study of an agricultural university

The present bibliometric study extends previous work by focusing on the research performance of departments in the natural and life sciences, the social and behavioral sciences, and the humanities. The present study covers all 70 departments from one agricultural university, and several veterinary departments of a second university. The impact analysis was extended by including other types of documents than journal articles. For about a third of the departments, publications not covered in citation indexes accounted for at least 30% of the citations to their total oeuvre. To deal with different citation and publication habits in the various fields, both short-term and medium-term impact assessments were made. The commonly used three year window is not universally applicable, as our results show. The inclusion of self-citations forms an important source of error in the ratio of actual/expected impact. To cope with this, the trend and level of self-citations was compared at university level with that in a matched sample of publications. Moreover, at a departmental level, self-citation rates were used to detect departments with divergent levels of self-citation. The expected impact of journals accounted for only 18% of the variance in actual impact. Comparison of bibliometric indicators with two peer evaluations showed that the bibliometric impact analyses provided important additional information.     

A macro study of self-citation

This study investigates the role of self-citation in the scientific production of Norway (1981-1996). More than 45,000 publications have been analysed. Using a three-year citation window we find that 36% of all citations represent author self-citations. However, this percentage is decreasing when citations are traced for longer periods. We find the highest share of self-citation among the least cited papers. There is a strong positive correlation between the number of self-citations and the number of authors of the publications. Still, only a minor part of the overall increase in citation rates that can be found for multi-authored papers is due to self-citations. Also, the share of self-citation shows significant variations among different scientific disciplines. The results are relevant for the discussion concerning use of citation indicators in research assessments. This revised version was published online in August 2006 with corrections to the Cover Date.     

Author self-citations in the field of ecology

Ecologists writing research articles frequently cite their own papers. Self-citations are frequent in science, but the reasons behind abnormally high rates of self-citations are questionable. My goals were to assess the prevalence of author self-citations and to identify the combination of attributes that best predict high levels of self-citations in ecology articles. I searched 643 articles from 9 different ecology journals of various impact factors for synchronous (i.e., within reference lists) and diachronous (i.e., following publication) self-citations, using the Web of Science online database. I assessed the effect of the number of authors, pages, and references/citations, the proportion of diachronous/synchronous self-citations, and the impact factor, on the proportion of synchronous and diachronous self-citations separately. I compared various candidate models made of these covariates using Akaike’s Information Criterion. On average, ecologists made 6.0 synchronous self-citations (12.8% of references), and 2.5 diachronous self-citations (25.5% of citations received 2.8 to 4.5 years after publication) per article. The best predictor of the proportion of synchronous self-citations was the number of authors. My study is the first to report recidivism in the inclusion of self-citations by researchers, i.e., the proportion of diachronous self-citations was best explained by the proportion of synchronous self-citations. The proportion of self-citations also increased with the number of pages and the impact factor of ecology journals, and decreased with the number of references/citations. Although a lot of variance remained unexplained, my study successfully showed regularities in the propensity of ecologists to include self-citations in their research articles.     

Self-citations at the meso and individual levels: effects of different calculation methods

This paper focuses on the study of self-citations at the meso and micro (individual) levels, on the basis of an analysis of the production (1994–2004) of individual researchers working at the Spanish CSIC in the areas of Biology and Biomedicine and Material Sciences. Two different types of self-citations are described: author self-citations (citations received from the author him/herself) and co-author self-citations (citations received from the researchers’ co-authors but without his/her participation). Self-citations do not play a decisive role in the high citation scores of documents either at the individual or at the meso level, which are mainly due to external citations. At micro-level, the percentage of self-citations does not change by professional rank or age, but differences in the relative weight of author and co-author self-citations have been found. The percentage of co-author self-citations tends to decrease with age and professional rank while the percentage of author self-citations shows the opposite trend. Suppressing author self-citations from citation counts to prevent overblown self-citation practices may result in a higher reduction of citation numbers of old scientists and, particularly, of those in the highest categories. Author and co-author self-citations provide valuable information on the scientific communication process, but external citations are the most relevant for evaluative purposes. As a final recommendation, studies considering self-citations at the individual level should make clear whether author or total self-citations are used as these can affect researchers differently.     

The influence of international collaboration on the impact of research results

There is an ongoing discussion on the influence of international collaboration on impact as measured by citation-based indicators. Collaboration generally involves more authors than ‘no collaboration’ work and it is obvious that the phenomenon of self-citation will be stronger (there are more authors to cite themselves). Thus it can be seen as an important ‘amplifier’ of measured impact. Although this effect is certainly possible and already demonstrated recently, it should not be considered as the only or even major explanation of higher impact in the comparison between ‘no collaboration’ and international collaboration. Using data of an extensive bibliometric study of astronomical research in the Netherlands, we prove that higher rates of self-citation in international collaboration do not play any significant role as ‘impact amplifier’. The central point is that proper impact measurement must involve corrections for self-citations.     

The other side of the coin: The intricacies of author self-citations

The present study views author self-citations, as a blend of experience and cognition of authors. This paper supports to lay down emphasis on consciousness and cognition of authors while assessing author self-citations. This revised version was published online in June 2006 with corrections to the Cover Date.     

Challenges in the study of Cuban scientific output

Cuban scientific output at macro level has not been frequently studied in the literature on scientometrics. The current paper explores the different metric approaches to the Cuban scientific activity carried out by national and international authors. Also, the article develops a scientometric study of the Cuban scientific production as included in Scopus during the period 1996–2007, using socio-economic indicators combined with bibliometric indicators supported by the SCImago Journal & Country Rank. Web of Science and Scopus are compared as information sources. Results confirm the possibility to use Scopus to obtain an objective picture of the Cuban science behaviour during the end of the 1990s and the beginning of the XXI century. The SCImago Journal & Country Rank, in this case, offers an important set of indicators. The combination of these indicators with those related to socio-economic aspects of activities in Science and Technology, allow the authors to show a perspective of the Cuban science system evolution during the period analyzed. The inclusion in Scopus of less-cited journals published in Spanish language and its impact on productivity and citation-based indicators is also discussed. Our investigation found an increasing growth of the Cuban scientific production during the whole period, which is in correspondence to the country efforts and expenditures in Research and Development activities.     

Some citation-related characteristics of scientific journals published in individual countries

Relationships between publication language, impact factors and self-citations of journals published in individual countries, eight from Europe and one from South America (Brazil), are analyzed using bibliometric data from Thomson Reuters JCR Science Edition databases of ISI Web of Knowledge. It was found that: (1) English-language journals, as a rule, have higher impact factors than non-English-language journals, (2) all countries investigated in this study have journals with very high self-citations but the proportion of journals with high self-citations with reference to the total number of journals published in different countries varies enormously, (3) there are relatively high percentages of low self-citations in high subject-category journals published in English as well as non-English journals but national-language journals have higher self-citations than English-language journals, and (4) irrespective of the publication language, journals devoted to very specialized scientific disciplines, such as electrical and electronic engineering, metallurgy, environmental engineering, surgery, general and internal medicine, pharmacology and pharmacy, gynecology, entomology and multidisciplinary engineering, have high self-citations.     

Two-phase edge outlier detection method for technology opportunity discovery

It has been observed that Southeast Asian countries and universities have ranked poorly in global research productivity and impact. The same is true for the field of language and linguistics. Some studies revealed that productivity and citation patterns in this field are lower compared to other fields of study. Thus, this study sought to examine the research performance of SEA countries and universities in the field of language and linguistics for efficient policy-making. The research performance of each SEA country and university was assessed through Scopus database using the following bibliometric indicators: total number of publications (P), total number of citations excluding self-citations (C), citations per publication (CPP), percent of non-cited articles (%PNC), and h-index. Findings revealed that SEA countries have only produced almost 2 % of all published articles in language and linguistics and around 1 % share in overall worldwide field citations. Interestingly, both the SEA countries and universities exhibit a trend toward increasing their yearly research productivity and citations. However, research productivity and citations in the field of language and linguistics are dominated by selected universities in each country particularly in Brunei, Singapore, Malaysia, and the Philippines. This study has implications for research policy-making and future studies.     

To cite or not to cite: author self-citations and the impact factor

Author self-citations are another factor that affects the impact factor of a journal. Typically these self-citations are just counted as such. But to be more meaningful I suggest that when examining the contribution of authors?? self-citations to impact factors one should first count the number of citations in the text rather than in the reference list, and then discriminate between different kinds of author self-citations??from those that are informative to those that are self-enhancing??if these data are to be more credible.     

Language biases in the coverage of the Science Citation Index and its consequencesfor international comparisons of national research performance

Empirical evidence presented in this paper shows that the utmost care must be taken ininterpreting bibliometric data in a comparative evaluation of national research systems. From theresults of recent studies, the authors conclude that the value of impact indicators of researchactivities at the level of an institution or a country strongly depend upon whether one includes orexcludes research publications in SCI covered journals written in other languages than in English.Additional material was gathered to show the distribution of SCI papers among publicationlanguages. Finally, the authors make suggestions for further research on how to deal with this typeof problems in future national research performance studies.     

Bibliometrics as a tool for measuring gender-specific research performance: an example from South African invasion ecology

Citations to published work are gaining increasing prominence in evaluations of the research performance of scientists. Considering the importance accorded to gender issues in South African science, it is surprising that (to our knowledge) no research has as yet ascertained the extent of sex differences in citations to the published work of scientists in this country. Our literature study shows that studies that have been conducted elsewhere tend to neglect in their analyses important gender-related and other factors, such as the sex composition of multi-authored papers and the extent of foreign co-authorship. Against this background, we illustrate the difficulties inherent in measuring the quality aspect of sex-specific research performance by means of an analysis of a dataset of articles (n = 229) that were published between 1990 and 2002 in the field of invasion ecology and in journals included in the Thomson Reuters Web of Science. Each article has at least one South African author address. The results indicate that foreign co-authorship is a better correlate of high citations than the sex of South African authors, and this is true irrespective of whether the annual citation rate or window period is used, whether or not self-citations are excluded, and whether or not the number of authors is controlled for by calculating fractional counts. The paper highlights these and other considerations that are relevant for future gender-focused bibliometric research, both in South Africa and beyond.     

Differences in the construction of sci based bibliometric indicators among various producers: A first over view

This contribution discusses basic technical-methodological issues with respect to data collection and the construction of bibliometric indicators, particularly at the macro or meso level. It focusses on the use of the Science Citation Index. Its aim is to highlight important decisions that have to be made in the process of data collection and the construction of bibliometric indicators. It illustrates differences in the methodologies applied by several important producers of bibliometric indicators: the Institute for Scientific Information (ISI); CHI Research, Inc.; the Information Science and Scientometrics Research Unit (ISSRU) at Budapest; and the Centre for Science and Technology Studies at Leiden University (CWTS). The observations made in this paper illustrate the complexity of the process of standardisation of bibliometric indicators. Moreover, they provide possible explanations for divergence of results obtained in different studies. The paper concludes with a few general comments related to the need of standardisation in the field of bibliometrics.     

Detecting <Emphasis Type="Italic">h</Emphasis>-index manipulation through self-citation analysis

The h-index has received an enormous attention for being an indicator that measures the quality of researchers and organizations. We investigate to what degree authors can inflate their h-index through strategic self-citations with the help of a simulation. We extended Burrell’s publication model with a procedure for placing self-citations, following three different strategies: random self-citation, recent self-citations and h-manipulating self-citations. The results show that authors can considerably inflate their h-index through self-citations. We propose the q-index as an indicator for how strategically an author has placed self-citations, and which serves as a tool to detect possible manipulation of the h-index. The results also show that the best strategy for an high h-index is publishing papers that are highly cited by others. The productivity has also a positive effect on the h-index.