This study investigated the application of a c-score, or composite citation indicator, to the field of ophthalmology, assessing its ability to capture noteworthy ophthalmology researchers and describing the population of high-ranking researchers as defined by the c-score. We chose the Weisenfeld Award to represent the ground truth for research impact in this study because it internationally recognizes “distinguished scholarly contributions to the clinical practice of ophthalmology,” which is corresponds to the subset of researchers included in our analysis whose primary research fields are listed as ophthalmology/optometry and clinical medicine. 11 Our method parallels several prior studies which use notable scientific awards as a gold standard for comparing the performance of citation metrics.8,10,15 We found that the c-score outperforms its constituent citation metrics in capturing Weisenfeld Awardees in its highest ranks. This finding suggests the c-score has a substantial correlation with subjective research impact derived from peer-review within the field of clinical ophthalmology. A likely explanation is that, compared to H-index and Hm-index, the c-score gives additional credit to first- and last- authors, who often represent people who contribute significantly to the field of ophthalmology.
In addition to evaluating the c-score, this study also described the population of approximately 3,000 clinical ophthalmology researchers among the top 100,000 scientists ranked by c-score from 2017–2021. Among all authors, the strongest correlations in citation metrics were seen between c-score and Hm. The main difference between these two indicators is that c-score incorporates slightly more impact from first and last authorship. Because the c-score captured more Weisenfeld awardees in its top ranks, it is likely that it reflects ophthalmology peer-review more accurately than Hm.
When considering the career lengths of authors included in this study, authors in the top 50 as ranked by c-score tended to have longer career lengths. While this is unsurprising, it was notable that the significance of disparity between career length in the top 50 vs non-top 50 increased from 2017 to 2021, while the mean career length of all ophthalmologists included in the database increased. A larger difference in career length between the top 50 and other researchers could have reflected an increasing pool of young ophthalmology researchers in the overall database, but this explanation is contradicted by an increase in the average career length from 2017–2021. Another possible explanation is that the advantage offered by a longer career simply increased from 2017 to 2021. The change in percentile was consistently different between the top 50 and other authors, with the top 50 generally experiencing less percentile shift from year to year. This is reasonable, as the top 50 authors’ ability to climb in rank is naturally limited, and their ability to fall in rank is limited by their existing research impact.
With regards to self-citation rate, a very small negative association was observed between self-citation percentage and c-score. This may suggest self-citation rate can positively influence a researcher’s impact; however, the size and significance of this association greatly limits its meaning. This is consistent with previous studies, which show minimal differences in self-citation rate across groups of scientists with a great range of reputability.10,16
Between the top 50 authors and other authors, female authors comprised between one sixth and one fifth of all researchers, with a slight increase in representation from 2017 to 2021. This proportion of women is generally smaller than that reported by other studies into gender balance in ophthalmology, which report that women comprise 20% of all ophthalmologists17, 25% of ophthalmology award recipients14, and 33% of authors in clinical ophthalmology journals.18
This study utilized a limited sample of authors selected by their having the highest c-score as defined by Ioannidis et. al.10 Our comparison of multiple citation indices is inherently limited by the inclusion criteria for the database we analyzed: authors were chosen for belonging to the upper echelon of all authors as ranked by c-score alone, which may exclude authors who have low c-scores but rank highly in other citation metrics. Additionally, all citation metrics we considered are limited by the data enumerated in Scopus, which does not include forms of research impact such as patents, book sales, and political influence. Beyond the author-specific data was pulled directly from the Ioannidis database, gender assignments were generated with GenderAPI. This software is limited by its corpus of non-English names (among the top 50 authors, only one name was misclassified, and the author had an Asian name) and its solely binary gender assignment. However, it is regarded as the most accurate automated gender assignment application, and the broad trends it finds over a thousand-plus names are likely reliable.13,14,19 Our evaluation of citation metrics’ performance was based on the Weisenfeld Award, which was chosen as an indicator for scientific achievement in the field of clinical ophthalmology. However, its selection relies on some subjective peer-review, and there is no perfect gold standard for research impact.
The professional relevance of citation index has contributed to the creation of numerous bibliometric strategies for capturing an individual’s research impact in a single number. This is the first investigation into applying the c-score, a composite citation indicator, to the field of clinical ophthalmology research. We found that among close to 5,000 ophthalmology researchers belonging to the top 100,000 researchers by c-score, most are male and American, and the higher-ranked authors tend to have longer career lengths. By assessing the c-score’s ability to capture Weisenfeld Awardees, we found that the c-score more completely captures winners of peer-review-based awards compared to its constituent citation indices, thus showing promise in accurately describing individuals’ research impact in clinical ophthalmology.