Journal self-citation has received significant attention recently (Chorus; Waltman, 2016; Gazni; Didegah, 2021; Heneberg, 2016; Taşkin et al., 2021; Wilhite; Fong, 2012). This interest may have originated from the perception that self-citations, and not the growth of impact, may be the main reason for the increase in indicators of some journals (Campanario, 2018; Heneberg, 2016). This alerted the need to identify self-citation patterns in databases and analyze journals with excessive self-citation rates (Gazni; Didegah, 2021; Taşkin et al., 2021; Yu; Yu; Wang, 2014).

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.

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.

Figure 3. Source: Research data.

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.

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%.

Figure 4. Source: Research data.

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.

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.

Figure 5. Source: Research data.

The mean SCRs by area were 6.28% for Engineering (ENG), 6.24% for the Exact and Natural Sciences (E&N), 5.36% for the Agricultural Sciences (AGS), 5% for Multidisciplinary (MTD), 5.12% for Health Sciences and Medicine (HS&M), 4.31% for Arts and Humanities (A&H), and 4.17% for Social Sciences (SSC). The overall mean was 4.83%.

The highest median SCRs were those of the AGS (3.89%), E&N (3.68%), ENG (3.62%), and HS&M (3.33%) journals. The areas of MTD (2.33%), SSC (2.48%), and A&H (2.74%) had the lowest median SCRs.

This difference between the two centrality measures in all areas may have been caused by outliers, i.e., publications with discrepant rates. However, discrepant SCRs were a minority, as 88.31% of journals had less than 10% of self-citations.

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.

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.

Figure 6. Source: Research data.

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.

Figure 7. Source: Research data.

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.

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.