In the gold open-access model, reading the publications is free and the publication costs, collected through the Article Processing Charge (APC), are incurred by the authors, their institutions, and funding bodies. A predatory journal will exploit this model to its own benefit with an inexistent or practically inexistent peer-review process. Selective databases, such as Scopus, PubMed, and Journal Citation Reports (JCRs), form an index of journals, a sort of whitelist that is used for the purposes of assessing researchers and taking decisions on grant funding. However, some articles from some predatory journals are in fact indexed, both in PubMed and in Scopus.
This investigation is centred on JCRs, perhaps the most prestigious and best recognized database in academia with the widest use at a global level, in order to analyse MDPI. MDPI has been open to question, a dubious publisher that has been moving within a ‘grey zone’. It is deserving of further analysis that will help us to determine whether it is using a broad range of questionable tactics that are neither illegal nor easy to detect.
JCR-indexed MDPI journals (edition 2018) were selected for the analysis (53 out of 218). As a control group for comparison, leading journals in each category were selected. The first relevant fact of the analysis is that some journals use very similar names to the journals with established reputations, one of the characteristics of predatory journals, with which they prey upon younger researchers and those less well informed on the subject of predatory journals. This is the case, e.g. of the MDPI journals Cells, Cancers, Polymers, Remote Sensing, Animals and Genes, remarkably similar to other journals established earlier and edited by Elsevier (Cell, Polymer, Gene, Remote Sensing of Environment), Wiley (Cancer), and Cambridge University Press (Animal).
The impact factors of all journals were reduced when self-citations were removed. The drop in the impact factor ranged between 38.96% in the case of Sustainability to 0.68% in Medicina with an average reduction of 14.8% in the value of the journal impact factor following the removal of self-citations. According to Clarivate, self-citation in the Web of Science ranges from 0% to 15%. Sustainability and Electronics journals showed exceptionally high self-citation rates (27.69% and 27.46%, respectively) followed by Minerals (26.15%). All journals, except the International Journal of Molecular Science, increased self-citation rates between 2018 and 2019 (between 35.33%, Symmetry, and 681.94%, Insects).
Shedding further light on MDPI-journal citing sources, the top 10 MDPI journals for citations listed on the Web of Science (WOS) were analysed and intra-MDPI citation levels were identified with other MDPI-journals. In 2019, almost all 53 MDPI-journals under analysis had intra-MDPI citation rates well above 20% (all except Universe, with 11.87% intra-MDPI citation rate, and Catalysts, with 18.73%), reaching values as high as 56.94% in Electronics, 51.07% in the ISPRS International Journal of Geo-Information (IJGI), 47.56% in Remote Sensing, and 46.55% in Sustainability.
If our attention is focussed on the intra-MDPI citation rate trends between 2018 and 2019, we see that 46 out of the 53 journals increased their intra-MDPI citation rates. However, the seven journals that never did (Sustainability, Mathematics, International Journal of Molecular Sciences, Symmetry, Applied Sciences, Micromachines, and Catalysts) had intra-MDPI citation rates above 15%, ranging from 18.73% in Catalysts to 46.55% in Sustainability.
The promotion of questionable special issues is one of the identifying characteristics of predatory journals. Certainly, the number of special issues published or scheduled yearly reveals no quality-related information, although the fact that the number of special issues in MDPI journals is so much higher than the number of ordinary issues per year inevitably awakens suspicions of a lucrative business aim. Since APC-based Open Access publishing involves remunerating publishers based on how many articles they publish, this can underpin perverse incentives to accept as many articles as possible to maximize revenue, so predatory journals operate in such a manner, eschewing legitimate peer review or other types of quality control and prompting an excessive publication of articles, often of inferior quality.
The results presented above showed that the 53 MDPI-journals under analysis possess, to a greater or lesser degree, some of the criteria for the identification of predatory journals and deviate from best editorial and publication practices when e.g. mimicking names and claiming rapid publication. The COPE/DOAJ/OASPA/WAME Principles for Transparency and Best Practices in Scholarly Publishing stipulate that journal names should not be easily confused with another journal and that journal websites should not guarantee very short peer-review times (as a member of COPE and DOAJ, MDPI could hardly argue that it ignores those Principles). Additionally, the constant and quite exceptional increase in the number of articles published in MDPI-journals between 2018 and 2019, reinforced by an exponential increase in the number of special issues, which easily outweigh the number of regular publications (above all in view of the previsions for 2020), together with an opportune increase in APC fees all raises serious concerns over the legitimacy of MDPI as a publisher, at the very least because its APC-based business model alters the economic and scientific incentives in academic publishing.
Reference
M Ángeles Oviedo-García. Journal citation reports and the definition of a predatory journal: The case of the Multidisciplinary Digital Publishing Institute (MDPI), Research Evaluation, 30(3), 2021, 405–419. https://doi.org/10.1093/reseval/rvab020
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