In recent years, the h-index has become a popular citation metric influencing a scientist’s research more than the impact factor. Despite this, the two metrics differ even if they have an impact on the research outcome. The h-index is named so after the physicist Jorge Eduardo Hirsch who invented it in 2005 for quantifying a researcher’s productivity in research based on publications.
Why is the h-index different from the impact factor?
The h-index is a quantitative measure to estimate an author’s scientific output based on the number of research articles published in a given year and their citations. On the contrary, the impact factor evaluates the journal’s reputation based on the total number of articles cited in the specific journal in the previous two years.
Hence, the impact factor measures the prestige of a journal, while the h-index measures the individual author’s research output.
How can the h-index be calculated?
The h-index can be defined as the total number of published papers (Np) of a researcher that have been cited a number of times (Nc) by each paper (j) over n number of years.
For example, if a researcher’s h-index is 9, it conveys that the researcher has published nine or more papers, for at least 9 of them have been cited nine times. Taking another example, if a scientist has published 23 articles, of which 16 have been cited 16 times at least, and then the scientist’s h-index is 16.
Advantages of h-index:
- An easy-to-calculate measure and objective in nature.
- A better accurate metric than the impact factor.
- It combines the outcome and the impact of a researcher, hence scores based on single-number measures such as citations per paper, number of highly cited articles, and the total number of citations.
- Exclusion of poorly cited articles and do not give an inaccurate inflated score.
- Useful for senior scientists with good publication records displaying their research and its effects in a positive manner.
Disadvantages of h-index:
- Scientists across disciplines cannot be compared based on the h-index as there are variations observed in terms of outcomes and research patterns.
- Young researchers might have drawbacks as the outcomes and impact increase gradually with time.
- In an article, it does not pay attention to the number of coauthors and their individual contributions, as it gives equal credit to all the authors of the particular article.
- Self-citations are not disregarded, which might give an inflated score.
- A researcher with a few highly cited papers may have a similar h-index to someone with numerous low-impact papers because the h-index ignores highly cited papers.
It is a good and advisable practice to keep a record of the number of papers published along with the citations so as to keep track of self-reputation and research efforts toward better outcomes.