Journal self-citation on the h5-index of Ibero-American journals

Abstract: It aims to analyze journal self-citation in Ibero-American journals from the h5-index of the Google Scholar Metrics. The bibliometric tool Gsm_hdata was used to identify 4049 Ibero-American journals indexed simultaneously in Latindex and Google Scholar Metrics. Self-citations were identified, self-citation rates by country and research area were calculated, and the h5-index was recalculated without self-citations (hs5-index). No self-citations were identified in almost 40% of the journals, especially those with an h5-index lower than 5. The overall average self-citation rate was 3.6%. Among the 1859 most cited journals with at least one self-citation, the rate was 4.8%, lower than that of research based on the Impact Factor. Journals of Engineering, Exact and Natural Sciences, and Agricultural Sciences had the highest self-citation rates, while Social Sciences and Humanities journals presented the lowest. Journals with excessive rates (outliers) were identified in all areas. These results suggest that the prior exclusion of journal self-citations in the calculation of the h5-index is not necessary. However, monitoring journals with excessive self-citation rates is recommended to avoid distortions in impact assessment procedures based on h5-index of Google Scholar Metrics.

Identifying the average and growth rates of self-citations (Chorus; Waltman, 2016) makes it possible to draw a parameter in impact assessment processes.Normal rates reflect the source identity of the citing work and the work cited, which is natural when there is a thematic relationship.Normal rates do not produce significant changes to indicators or sudden changes in position in rankings, strata, or quartiles of databases (Flatt;Blasimme;Vayena, 2017;Yu;Yu;Wang, 2014).Journal self-citations are accepted in science when they perform their function, i.e., provide information about works previously published in the same journal.
Journal self-citation rates considered abnormal should be analyzed and, if possible, justified.They may be more frequent in journals with low visibility or from specialized areas (Sanfilippo et al., 2021).They may also originate from a specific document (an editorial or review article) that contains many self-citations.However, abnormal self-citation rates may also indicate editorial practices to boost impact indicators (Wilhite;Fong, 2012;Yu;Yu;Wang, 2014).
The Impact Factor (IF) and other impact indicators based on the average number of citations per article is sensitive to the increase in citations received (Gazni;Didegah, 2021;Liu;Fang, 2020;Waltman, 2016).Thus, journal self-citations have become a path to increase impact (Taşkin et al., 2021).The IF version that excludes self-citations facilitates large-scale analyses, particularly identifying rates by research areas.Due to this ease of data extraction and analysis, most self-citation studies use data from the Journal Citation Reports (JCR) (Huang;Cathy Lin, 2012;Yu;Yu;Wang, 2014).
Although the h-index is not so sensitive to excess citations -including self-citations (Hirsch, 2005;Waltman, 2016) -the influence of journal self-citations on the h5-index result is not well known.Most studies based on the h-index have focused on author self-citations (Bartneck;Kokkelmans, 2011;Schreiber, 2009;Vîiu, 2016), the original unit of analysis of this indicator (Hirsch, 2005).
Google Scholar (GS) ignores the existence of self-citations in its two extensions dedicated to citation analysis: Google Scholar Citations (GSC) and Google Scholar Metrics (GSM).There is no resource for identifying self-citations, and the bibliometric indicators of these sources (i10-index, h5-index, h5-median) record citations and self-citations as a single element (López-Cózar;Cabezas-Clavijo, 2013;Jacsó, 2012).
In this sense, an analysis of self-citations of Ibero-American journals from GSM data.The self-citation rates were calculated by the country of origin of the journals and by area of knowledge.
The h5-index was recalculated after excluding self-citations.The journals were classified with normal and abnormal (outliers) self-citation rates.
The proposal is justified by the fact that GSM has been considered an alternative source of impact analysis, especially for journals not indexed in JCR and Scopus, which are the majority in the Ibero-American context (López-Cózar;Cabezas-Clavijo, 2013;Jacsó, 2012).
The results can help to answer the following questions: what are the average self-citation rates of Ibero-American journals from h5-index data?Do journals with high self-citation rates perform better on the h5-index than journals with normal rates?Is excluding self-citations in impact assessment processes necessary based on the h5-index?
Additionally, the findings can also help to enhance the understanding the influence of journal self-citations on the h-index, an alternative indicator to the traditional IF and CiteScore (CS) that has been gaining space in the scenario of impact assessment of Ibero-American scientific production.

Journal self-citation
Self-citation is defined as the practice of an author citing a previous work of their authorship or co-authorship (Ioannidis, 2015;Heneberg, 2016;Waltman, 2016;Szomszor;Pendlebury;Adams, 2020;Taşkin et al., 2021).However, self-citation may be configured in other ways, such as at the collaboration level by citing research colleagues, at the journal level by citing articles from the same journal (Rousseau, 1999;Hartley, 2009), at the institutional level by citing a publication from the same institution/publisher or scientific peers (Zhou, 2021), at the country level by citing a publication from the same country (Huang;Cathy Lin, 2012;Frandsen, 2007;Waltman, 2016), and so on.
There is no unanimity regarding excluding self-citations in impact indicators (Campanario, 2018;Huang;Cathy Lin, 2012).There is a consensus that at the micro (author, journal) and meso (institution) levels, the influence of self-citation on the impact analysis is significant (Yu;Yu;Wang, 2014), and exclusion may be necessary.In turn, at the macro level (country), the influence is not significant, and the exclusion is unnecessary (Waltman, 2016).However, it is unanimous that the existence of self-citations in scientific communication cannot be ignored (Frandsen, 2007).
Unlike author self-citation, in which there is an unequivocal intention to self-cite (whether justifiable or not), journal self-citation may occur involuntarily (Hartley, 2009).It is not uncommon for several studies on the same topic to be published in the same journal.Thus, the citation of part of these studies in new work in the same publication is scientifically valid (Frandsen, 2007;Yu;Yu;Wang, 2014;Gazni;Didegah, 2021).
The problem begins when self-citation is unnecessary and there is no thematic or methodological relationship between the citing work and the work cited.Unnecessary or excessive self-citations are indicators of abnormality that may affect the credibility of the research and the publication itself.In excess, journal self-citations may interfere with the impact assessment, artificially increasing citation-based indicators (Bartneck;Kokkelmans, 2011;Yu;Yu;Wang, 2014).
In 2007, the IF started to have a version excluding self-citations.In 2009, the JCR began to identify and monitor self-citations of indexed publications.Several publications suffered sanctions of Clarivate Analytics due to irregularities involving self-citations in the IF (Huang;Cathy Lin, 2012;Liu;Fang, 2020).
At the same time, new impact indicators were created based on the exclusion of self-citations, such as the Eigenfactor Score (ES) and the Article Influence Scores (AIS) (Bergstrom;West;Wiseman, 2008) or based on the limitation of self-citations, such as the Scientific Journal Rankings (SJR) (González-Pereira;Guerrero-Bote;Moya-Anegón, 2010).These indicators assume that self-citations interfere with the impact or influence of the publication in its scientific field.
The differentiation between citations and self-citations facilitated large-scale studies, especially identifying self-citation patterns or rates.Journal self-citation rates are defined in two ways.The first, self-citing, is defined by the percentage of self-citations among the total number of references in a journal.The second, self-cited, by the percentage of self-citations in the total number of citations received by a journal (Rousseau, 1999;Frandsen, 2007).
Self-citation rates are established at different levels.They may be calculated by journal, discipline or research area, publisher or institution, language, and country (Taşkin et al., 2021).
The self-citation rates are higher soon after the publication of the work, decreasing their occurrence over the years.They tend to be higher in journals of lower impact (Heneberg, 2016), regional languages (Taşkin et al., 2021), specialized subjects (Livas;Delli, 2018;Sanfilippo et al., 2021), and areas of lower visibility (Rousseau, 1999;Frandsen, 2007).
On the other hand, the average self-citation rates do not seem to show relevant differences among subject categories, remaining at close percentages in studies of different disciplines (Taşkin et al., 2021).
A study of 5876 journals indexed in the 2002 JCR found that 82% of the publications had rates lower than 20%, with a general self-citation average of 5.87% and a median of 9%.These JCR patterns do not appear to have varied in the following years.
A new study conducted in 2018 with 11866 journals indexed in the JCR found that approximately 10% had 25% or more self-citations, and 5% did not have any self-citations.The average self-citation rates, from 5% to 10%, increase as the quartile of publications decreases, i.e., they are higher in publications of lower impact (Taşkin et al., 2021).
The self-citation rates of 35 intensive care medicine journals range from 0% to 35.4%, with a median of 8.8% (Sanfilippo et al., 2021).The rates of 85 dentistry journals decreased from 13.725% in 2014 to 10.667% in 2016 (Livas;Delli, 2018).In both studies, the journals of specific subjects in each discipline recorded higher rates than those of broad scopes (Livas;Delli, 2018;Sanfilippo et al., 2021).
The research aimed to identify excessive journal self-citation patterns.Usually, rates higher than 20% or 25% are considered excessive, regardless of the area of knowledge.Even more extreme rates may indicate poor practices (Taşkin et al., 2021).However, self-citation rates above the discipline average, for example, are not necessarily due to manipulation Yu;Yu;Wang, 2014).The performance of large-scale analyses is recommended for a more accurate assessment (Frandsen, 2007).
Poor journal self-citation practices may be voluntary (anticipated) or coercively induced (Chorus; Waltman, 2016).In the first case, the authors voluntarily insert self-citations imagining that this may facilitate the acceptance of the manuscript by a given journal.In the second case, the editors or reviewers require or strongly recommend that the authors cite one or more works from the journal (Chorus; Waltman, 2016;Wilhite;Fong, 2012).
In these two forms, voluntary or coercive, journal self-citations have, as a direct consequence, the artificial (abnormal) increase in impact indicators based on the frequency of citations received (Ioannidis, 2015).

Hs5-index
Unlike with the IF, journal self-citation studies from h-index data are rare.A possible reason for this gap is that only the most cited articles are considered in calculating this indicator (Barnes, 2017).It is estimated that only 5% of the total articles published by an author or a journal integrate the h result.Thus, in theory, self-citations could interfere with the h-index to a lesser extent than with indicators based on the average citations, such as the IF and CS (Hirsch, 2005;Waltman, 2016;Barnes, 2017).
A version of the h-index without self-citations called the hs5-index was proposed by Schreiber (2009).This proposal was based on the perception that, contrary to what Hirsch (2005) imagined, self-citations can influence the outcome, especially in the case of extreme self-citation rates (Vîiu, 2016).However, this proposal, as most studies on self-citation based on the h-index, refers only to author self-citations (Vîiu, 2016;Teixeira da Silva;Dobránszki, 2018).
The influence of journal self-citations on the h-Index, on the other hand, is not yet well known.In the case of Google Scholar Metrics (GSM), the inexistence of data analysis and extraction resources makes it challenging to carry out broader studies (López-Cózar; Cabezas-Clavijo, 2013).The lack of standardization of titles (Harzing, 2014) may also interfere with the analysis of the correspondence of the titles of citing and cited sources.
The lack of self-citation parameters may be an obstacle to using the h5-index in evaluation systems.Journals with excess self-citations may gain an advantage in defining impact levels (rankings, quartiles, or strata) over publications with normal self-citation rates.It is recommended to monitor self-citations in the h5-index to avoid manipulations.

Methodological procedures
This work presents partial results of the doctoral research by Canto (2022), carried out from 4049 Ibero-American journals indexed in the 2021 edition of the GSM, which has the h5-index calculated from articles published from 2016 to 2020 and citations registered until July 2021.
The procedures described refer to the processes of identification and analysis of journal self-citations.The Gsm_hscite resource was used to identify self-citations from the h5-index data of all journals in the research universe.
Gsm_hscite is the self-citation analysis feature of the Gsm_hdata tool (Canto, 2022).It performs the functions of identifying self-citations from GSM citation data and recalculating impact indicators.This feature calculates four indicators from the identified self-citations: the hs5-index (Schreiber, 2009), the hs5-median, the self-citation rate per article of the h5-index, and the self-citation rate per journal.
Gsm_hscite is configured to identify the main title and any equivalent titles, considering the non-standardization of titles in GSM.This configuration increases its accuracy because GSM does not standardize entries by journal titles.Equivalent titles may be indexed in the list of articles of the h5-index.
Figure 1 describes the operation of Gsm_hscite in a journal with title variations.
In a second moment, the list of articles that cite each article in the h5-core is accessed (5).A journal's titles (main and equivalent) are compared with the titles of the citing sources, recording the occurrence of journal self-citations (6), as shown in Figure 2.This process is repeated for all citations received by the articles of the analyzed journals.Finally, the h s 5-index and h s 5-median, the percentage rate of self-citations per article (article self-cited rate -ASR), and the percentage rate of self-citations per journal (self-cited rate -SCR) (Rousseau, 1999) are calculated.
The self-citation rate per journal was chosen as the primary indicator to represent the self-citation phenomenon, considering its recurrent use in related studies.
The self-citation rate per journal (self-cited rate) represents the percentage of self-citations relative to the total citations received by a journal, including self-citations (Rousseau, 1999).
The self-citation analysis was divided into two parts: a general analysis and a specific analysis.The general analysis included all journals in the research universe.The specific analysis was conducted only with journals of more significant impact with identified self-citations.
The selection of the journals analyzed in the second part was based on two criteria, one of exclusion and the other of inclusion: (1) exclusion of journals with a zero self-citation rate; (2) inclusion of publications with at least 50 citations, approximately, identified by the formula h5-index × h5-median = n, with n > 49.
This definition was intended to achieve greater statistical accuracy.It ensures that a self-citation implies a maximum percentage of 2% in the SCR, avoiding distortions in analyses by percentage values.
It also aims to avoid interference caused by publications that received few citations, in which case a self-citation may assume a high percentage.For example, in a publication with an h5-index = 2 that received five citations, only two self-citations would represent an SCR of 40%.

Results and discussion
Figure 3 shows the SCR distribution according to the h5-index of all journals in the research universe regarding the general analysis of self-citations.No self-citations were identified in 1586 journals, corresponding to 39.17%.Of the publications with SCRs equal to zero, it was identified that 1158 (73%) had an h5-index not higher than 5, i.e., they had a low level of impact.
On the other hand, SCRs greater than 20% were not detected in journals with an h5-index greater than 25.These data suggest that SCRs higher than the general limit of 20% set in previous studies (Taşkin et al., 2021) are more frequent in journals of low and intermediate impact levels, with an h5-index ranging from 5 to 25.
The median and mean SCRs of the h5-index for the whole set were 1.37% and 3.61%, respectively.These values are lower than those obtained in IF-based self-citation studies (Livas;Delli, 2018;Sanfilippo et al., 2021;Taşkin et al., 2021;Gazni;Didegah, 2021), in which the mean and median rates were around 5% and 8%, approximately.This indicates that self-citations less influence the h5-index than the IF, a characteristic that may be considered positive for using this indicator in evaluation processes.

Self-citation rate by country
The following analysis was conducted from a subset of journals that received at least 50 citations, approximately, with at least one self-citation.Application of these criteria resulted in identifying a subset of 1859 journals.
Upon analyzing self-citations by the country of origin of the journals, Figure 4 shows that Cuba had the highest SCRs, with a mean of 9.8% and a median of 5.6%.Brazil placed second, with a mean of 5.1% and a median of 3.9%.Both had journals with excessive SCRs, especially those above 30%.Brazil also published a journal with almost 100% self-citations.Colombia and Argentina presented a similar distribution, with median SCRs close to 3%.Colombia, however, had more outliers, especially with SCRs greater than 20%.Chile, Mexico, and Spain had the lowest median SCRs.However, Spain and the other countries had more outliers, including at rates exceeding 40%.
The data suggest that self-citation occurs more frequently in Cuban journals than in other countries in the region.On the other hand, journals with excessive SCRs were observed in virtually all countries.This finding requires attention to the practice of self-citation in journals in the region, especially those not indexed in the JCR and Scopus.
Indexed journals tend to control their SCR, given that both databases have citation monitoring mechanisms.

Self-citation rate by area
Figure 5 shows the SCR distribution according to the area of knowledge.The analysis is supplemented by calculating centrality measures (mean and median) by area.
These results confirm that the SCRs calculated based on the h5-index tend to be lower than those calculated from the IF (Taşkin et al., 2021).This reinforces the thesis of the lower susceptibility of the index to the influence of self-citations (Hirsch, 2005;Waltman, 2016), considering its sample formula based on the most cited articles.This may support arguments against the exclusion of self-citations in impact assessment.On the other hand, it would be difficult to defend the maintenance of the performance of journals that, notably, had a significant increase in performance due to the excess of self-citations.
Based on the premise that excessive self-citation should be monitored (Frandsen, 2007), the analysis compares journals with normal and excessive SCRs.Journals with normal SCRs are those within mean distribution levels.Journals with excessive SCRs are those statistically identified as outliers in journals with common characteristics, such as the same research area of knowledge (Figure 5) or the same country of origin (Figure 4).
The differentiation between normal and outlier SCRs thus stems from statistical analysis.No value judgment is made in the scope of this research about the reasons for any extravagant SCRs in the analyzed journals.

Variation between the h5 and hs5 indices
Figure 6 shows the average variation between the h5 and hs5 indices (VrH) in journals with normal and outlier SCRs of the entire subset of the specific self-citation analysis.
The outliers had a mean h5-index lower than the other journals, as reported in studies based on the IF (Heneberg, 2016;Taşkin et al., 2021).The difference is accentuated in the comparison using the hs5-index, with a mean decrease of 33.5% in the average impact of outliers, compared to a drop of less than 5% in other journals.This result indicates that the excess of self-citations may benefit journals and distort the results of evaluation processes based on the h5-index of the GSM.It is advisable to monitor self-citations and, based on this, set boundaries between normal and excessive SCRs.
Figure 7 shows that the outliers obtained an h5-index growth at a higher pace than the others in the last three editions of GSM (2019-2021).The cumulative advantage was 10% when the two measurements were combined.However, it is impossible to attribute all the additional growth of outlier journals to self-citations alone.However, based on the defined indicators, this justified the conduction of a more in-depth analysis, especially by comparing the average performance of journals with normal and outlier SCRs.

Conclusions
The results suggest that the h5-index is less susceptible to self-citations' influence than the IF.The calculation of the h-index results in disregarding a significant portion of the citations received by a journal, including self-citations.Some findings corroborated findings from previous studies.The areas with the highest SCRs were those with the fewest journals, i.e., the most specialized areas.This trend may be because more specialized areas form citation networks with lower density, which increases the probability of identity between the citing source and cited source, thus configuring journal self-citations.
Journals with higher SCRs had lower average impact levels.This indicates that self-citations may be a self-promotion strategy adopted by more recent publications that still lack recognition.A hypothesis to be tested in future studies is if, after an initial period with more self-citations, reaching an intermediate impact level can increase the proportion of external citations and decrease the SCR.
In general, the data supported the lack of a need for prior exclusion of journal self-citations in impact analyses based on the h5-index of the GSM, as advocated by part of the literature.
From another perspective, it has been shown that not excluding self-citations beforehand cannot lead to the total disregard of this parameter.It is necessary to monitor the SCR to prevent distortions, given that journals with statistically discrepant percentages were identified in all areas.
The resistance of the h5-index to self-citations decreases with discrepant rates.At the outlier level, self-citations can decisively interfere with impact levels, conferring an advantage compared to journals with moderate SCRs.This indicates the need for monitoring self-citations in the h5-index and, if necessary, correcting the results of evaluation indicators in some cases.Corrections may involve lowering the position in rankings, strata, or quartiles, adjusting the value of the h5-Index, or classifying journals as non-scientific, given the preponderance of self-citations relative to other citations.

Figure 3 -
Figure 3 -Distribution of self-citation rates according to the h5-index.Source: Research data.

Figure 4 -
Figure 4 -Distribution of self-citation rates by country.Source: Research data.

Figure 5 -
Figure 5 -Distribution of self-citation rates by area.Source: Research data.

Figure 6 -
Figure 6 -Variation between the h5-index and h s 5-index.Source: Research data.

Figure 7 -
Figure 7 -Growth rate of the h5-index.Source: Research data.