Self-citation quantified

I always feel a little bit bad when I have to cite my own prior work for a new research paper. As scientists develop career trajectories, self-citation becomes inevitable. Early work often becomes a foundation for later work. The point of citation is to credit the work that allows you to advance; we track citations so that we can see more clearly which research efforts have led to further advances.

And so, most successful scientists will often cite their own earlier work. The more entrenched an individual’s research trajectory becomes, the higher ratio of self-citation to citation of other research will be.

A new study in PLoS Biology by John Ioannidis and coworkers develops a citation metrics author database that facilitates seeing which authors cite themselves the most often: “A standardized citation metrics author database annotated for scientific field”.

Nature comments on the study, focusing on the issue of self-citation: “Hundreds of extreme self-citing scientists revealed in new database”

The data set, which lists around 100,000 researchers, shows that at least 250 scientists have amassed more than 50% of their citations from themselves or their co-authors, while the median self-citation rate is 12.7%.
The data are by far the largest collection of self-citation metrics ever published. And they arrive at a time when funding agencies, journals and others are focusing more on the potential problems caused by excessive self-citation. In July, the Committee on Publication Ethics (COPE), a publisher-advisory body in London, highlighted extreme self-citation as one of the main forms of citation manipulation. This issue fits into broader concerns about an over-reliance on citation metrics for making decisions about hiring, promotions and research funding.
“When we link professional advancement and pay attention too strongly to citation-based metrics, we incentivize self-citation,” says psychologist Sanjay Srivastava at the University of Oregon in Eugene.

When it comes to judging the impact of individual scientists, people are very sensitive to possible ways of “cheating the system”, and self-citation is widely perceived to be one of those ways. But actually Ioannidis and coworkers find that separating self-citation from total citation counts doesn’t change much when it comes to highly-cited researchers. There are some outliers, but they are focused in particular countries, fields, and institutions.

Another aspect of Ioannidis and colleagues’ study is quantifying the citation practices in different fields of study. Anthropology as a field is not separated out in their table, but social sciences generally have low citation numbers—less than half the numbers of biology or clinical sciences. The 90th percentile for total citations in the social sciences is 423, meaning that only 10% of researchers have career citation totals of more than that.

As a result, methods of judging scientific output that rely upon citation counts tend to underestimate the impact of social scientists. Most kinds of scientific assessment look within fields rather than across them, but in some of the cross-disciplinary organizations (like national academies) social scientists are under-represented compared to their impact in ways other than citations.