Suitability of H- and X-indices for Evaluating Authors' Individual Research Achievements in a Given Short Period of Years: A Bibliometric Analysis

Background: The h-index of a researcher refers to the maximum number h of his/her publications that has at least h citations via the concept of the square area. The x-index is determined by the maximum area of a rectangle under the curve to interpret authors' individual research achievements (IRAs). However, the properties of both metrics have not been compared and discussed before. This study aimed to investigate whether both metrics of h- and x-index are suitable for evaluating IRAs in a short period of years.

Methods: By searching the PubMed database (Pubmed.com), we used the keyword "PLoS One" (journal) and downloaded 50,000 articles published in 2015 and 2016. A total of 146,346 citations were listed in PubMed Central and 27,035 authors(with h-index ≥1) were divided into 3 parts. Correlation coefficients among metrics (ie, AIF, h, g, Ag, and x-index) were examined. The bootstrapping method used for estimating 95% confidence intervals was applied to compare differences in metrics among author groups. The most cited authors and topic burst were visualized by social network analysis. The most prominent countries/areas were highlighted by the x-index and displayed via choropleth maps.

Results: Results demonstrated that, first, the h-index had the least relation to other metrics and failed to differentiate authors' IRAs among groups, particularly in a short time period. Second, the top 3 highest x-index for countries were the United States, China, and the UK but with the productivity-oriented feature. Third, the most cited medical subject headings (ie, MeSH terms) were genome, metabolome, and microbiology, and the most cited author was Lori Newman (whose x-index = 13.52, and h = 2) from Switzerland with the article (PMID = 26646541) cited 291 times. The need for the x-index combined with a visual map for displaying authors' IRAs was verified and recommended.

Conclusions: We verified that the h-index failed to differentiate authors' IRAs among author groups in a short time period. The x-index combined with the Kano map is recommended in research for a better understanding of the authors' IRAs in other journals or disciplines, not just limited to the journal of PloS One as we did in this study.