Release Date: August 28, 2013
Category: Scientific Writing
Author: Katherine A., Ph.D.
Your achievement as a researcher depends on your productivity and on the impact of your work on the scientific community. Your research productivity can be measured by the number of journal articles you publish, and your research impact can be measured by the number of citations your journal articles receive (i.e., the number of times your journal articles are included in the reference lists of other journal articles). These two aspects of your publication record can be combined into a single index, such as the h-index, which can be used to determine your rank relative to other researchers or to make decisions regarding your tenure or promotion.
Physicist Jorge E. Hirsch created the h-index to serve as a single number that can characterize a researcher’s scientific output. An index of h indicates that your h most highly cited articles have at least h citations each. For example, imagine that you have published four journal articles. Your first article has been cited 10 times, your second article has been cited 7 times, your third article has been cited 3 times, and your fourth article has been cited 2 times. Because you have three articles that have received at least 3 citations, your h-index is equal to 3. In the future, when your fourth article has received 4 citations, your h-index will be equal to 4. In this manner, the h-index simultaneously conveys information about your research productivity and impact.
Unlike impact factors, which are meant to measure the importance of particular journals, the h-index was designed to characterize the work of individual researchers. As the h-index is a combined measure of both research productivity and impact, it can be a highly useful indicator of scientific achievement. However, the h-index can also be misunderstood or misused. Therefore, there are several caveats to consider when interpreting the h-index.
For instance, the h-index can be inflated by self-citations (i.e., citing one’s own work). Although self-citations are often appropriate and even necessary for scientific communication, researchers who excessively cite their own work may artificially inflate their h-indices.
Researchers who have been publishing for longer tend to have higher h-indices. As such, the h-index may unfairly characterize the scientific output of younger researchers whose journal articles have not had time to accrue citations.
Also, the h-index does not account for the number of authors on each journal article or the order of authors. Researchers in disciplines in which many co-authors are common may publish more articles than researchers in disciplines in which sole authors are common, and multi-authored articles may receive a greater number of self-citations than single-authored articles. Also, the h-index gives equal credit to all co-authors on a journal article, even though, for example, the scientific contribution of the first author may be considerably larger than that of the fifth author.
Due to some perceived shortcomings of the h-index, several variations or alternatives to the h-index have been proposed. Below are a few more common alternative indices.
Several tools exist that make it easy for you to calculate your h-index and see who is citing your journal articles. Some of these tools are free, and others are available through fee-based institutional subscriptions. As there are variations in how the tools collect information, different tools may provide different citation counts and h-indices. Most notably, tools relying on Google Scholar information tend to give the highest h-index estimates.
Measuring the prestige of researchers using the impact factors of the journals in which they publish is a common error, as impact factors are meant to evaluate particular journals and not individual researchers. In contrast to impact factors, the h-index was specifically designed to assess the scientific output of individual researchers by simultaneously considering their productivity (i.e., number of articles) and the impact of their work (i.e., number of citations), with higher h-indices generally reflecting greater researcher success. Ranking researchers by their h-indices, however, should be done carefully, as there are several factors (i.e., length of research career, self-citations, disciplinary differences, etc.) apart from personal achievement that can influence h-index values. If you want to know your own h-index, several tools are available to help you to calculate your h-index and track your research impact over time. Therefore, when thinking about your success as a researcher, you should consider not only the impact factors of the journals in which you publish but also how much impact your journal articles have on the scientific community.
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