The h-Index for Associate and Full Professors of Dermatology in the United States: An Epidemiologic Study of Scholastic Production

Comment

Professional advancement in academic medicine requires scholastic production. The h-index, defined as the number of publications (h) that have been cited at least h times, is a bibliometric measure that accounts for both volume and impact of an individual’s scientific productivity. The h-index would be a useful tool for determining professional advancement in academic dermatology departments. In this project, we calculated h-index values for 300 associate professors and 352 full professors of dermatology in the United States. We found the median h-index for associate professors was 8 and the median h-index for full professors was 21. There was more than a 5-fold variation in median and mean h-indices between lower and upper quartiles within both the associate and full professor cohorts. The highest median and mean h-indices were found among full professors of dermatology in western states. These results provide the opportunity for academic dermatologists and institutions to compare their research contributions with peers across the United States.

Our results support those of John et al⁵ who also found academic rank in dermatology was correlated with h-index. Scopus, Web of Science, and Google Scholar can be used to calculate h-index, but they may return different scores for the same individual.⁶ John et al⁵ used the Scopus database to calculate h-index. We used Web of Science because Scopus only includes citations since 1996 and Web of Science was used in the original h-index studies by Hirsch.^1,2 Institutions that adopt h-index criteria for advancement and resource distribution decisions should be aware that database selection can affect h-index scores.

Caveats With the h-Index
Flaws in the h-index include inflationary effects of self-citation, time bias, and excessive coauthorship. Individuals can increase their h-index by routinely citing their own publications. However, Engqvist and Frommen⁷ found tripling self-citations increased the h-index by only 1.

Citations tend to increase with time, and authors who have been active for longer periods will have a higher h-index. It is more difficult for junior faculty to distinguish themselves with the h-index, as it takes time for even the most impactful publications to gain citations. Major scientific papers can take years from conception to publication, and an outstanding paper that is 1 year old would have fewer citations than an equally impactful paper that is 10 years old. To adjust for the effect of time bias, Hirsch² proposed the m-index, in which the h-index is divided by the years between the author’s first and last publication. He proposed that an m-index of 1 would indicate a successful scientist, 2 an outstanding scientist, and 3 a unique individual.²

The literature is increasingly dominated by teams of coauthors, and the number of coauthors within each team has increased over the last 5 decades.⁸ h-Indices will increase if this trend continues, making it difficult to compare h-indices between different eras. Prosperi et al⁹ found national differences in kinship-based coauthorship, suggesting nepotism may influence decisions in assigning authorship status. h-Index valuations do not require evidence of meaningful contribution to the work but simply rely on contributors’ self-governance in assigning authorship status.

The h-index also has a bias against highly cited papers. A scientist with a small number of highly influential papers may have a smaller h-index than a scientist with more papers of modest impact. Finally, an author who has changed names (eg, due to marriage) may have an artificially low h-index, as a standard database search would miss publications under a maiden name.

Limitations
This study is limited by possible operator error when compiling each author’s publication list through Web of Science. Our search and refinement methodology took into account that authors may publish with slight variations in name, in various subject areas and fields, and with different institutions and coauthors. Each publication populated through Web of Science was carefully verified by the principal investigator; however, overestimation or underestimation of the number of publications and citations was possible, as the publication lists were not verified by the studied associate and full professors themselves. Our results are consistent with the h-index bar charts published by John et al⁵ using an alternate citation index, Scopus, which tends to corroborate our findings. This study also is limited by possible time bias because we did not correct the h-index for years of active publication (m-index).

Conclusion

In summary, we found the median h-index for associate professors was 8 and the median h-index for full professors was 21. We found a broad range of h-index values within each academic rank. h-Index for upper-quartile associate professors overlapped with those of lower-quartile full professors. Our results suggest professional advancement occurs over a broad range of scholastic production. Adopting requirements for minimum h-index thresholds for application for promotion might reduce disparities between rank and scientific contributions. We encourage use of the h-index for tracking academic progression and as a parameter to consider in academic promotion.