G-index: A Metric for Evaluating the Scientific Impact of Researchers

The G-index is a metric that measures the impact of a scientist, based on the number and citations of their research works. Proposed by Leo Egghe in 2006, the g-index is considered an improvement over the h-index, addressing some of its limitations.

Method for Calculating the G-index

To calculate the g-index, first, a scientist's research works must be ranked in descending order by the number of citations. Then, determine the largest number g such that the first g publications have a total number of citations greater than or equal to g². For example, consider a scientist with 10 research works, ranked in descending order of citations as shown in the figure below. This scientist's g-index is 7, because the 7 publications with the highest number of citations have a total number of citations greater than or equal to 7² (i.e., 49).

Advantages and Limitations of the G-index

The G-index is considered an advancement over the h-index, with the following notable advantages:

• Reflects differences in citation distribution: The G-index helps differentiate scientists who have the same h-index but vary in citation distribution. For instance, two scientists, A and B, both have an h-index of 10. However, scientist A has 10 publications, each cited 10 times, while scientist B has one publication cited 100 times and the remaining 9 publications cited less than 10 times. In this case, A's g-index is 10, while B's is 19. This shows that B's work has a greater impact than A's.
• Encourages quality over quantity: The G-index encourages scientists to focus on the quality of their work rather than just pursuing quantity. To increase the g-index, it's necessary not only to increase the number of publications but also the number of citations for each publication. As a result, the g-index can help reduce the widespread publication of low-quality works merely to achieve a high h-index.

Despite its advantages, the g-index still has some drawbacks and is not as widely used as the h-index:

• Affected by objective factors: The G-index is still influenced by factors beyond scientific knowledge, such as the field of study, publication language, and publication time. Different research fields have varying levels of competition and scales, making it difficult to compare g-indexes across scientists from different fields. Similarly, works published in English generally have more opportunities to be cited than works in other languages. Furthermore, older works often have more citations than newer ones, so the g-index may favor established scientists over younger ones.
• Does not reflect the importance of individual works: The G-index does not reflect the individual importance and contribution of each research work. A work may have a significant impact on the development of a field or solve a critical problem, but if it is not widely cited, the author's g-index will remain low. Conversely, a work that is merely a review or assessment, but widely cited, will result in a high g-index for the author. Therefore, the g-index cannot replace the need to read and evaluate the quality of individual research works.

To look up an author's g-index, users can use the Publish or Perish software, a free citation analysis tool.