H-index explained

We hear a lot about the H-index, sometimes called the Hirsch index or Hirsch number after Jorge E. Hirsch, the guy who made it up.

The h-index attempts to measure both the productivity and impact of the published work of a scholar. So, quality and quantity.

It is sometimes applied to the productivity and impact of a group of scientists (such as a department,  university or country), and sometimes to a scholarly journal.

How is it calculated and what does it actually mean?
 
The h-index:

A scientist has index h if h of his/her N_p papers have at least h citations each, and the other (N_p-h) papers have no more than h citations each.

Well, if you list all of an author's publications from most cited to least cited, and number them, there will be a point where the number in the list is greater than the number of citations for that article, like this:

Paper 6 only has 4 citations, so this researcher's h-index is 5.

There are about a million problems with the h-index. It is still regarded as the single best measure for scholarly impact.
Some of the many things that can make the h-index misleading are:

• It doesn't take into account very highly cited papers. For example, another scholar could have a h-index of five, but have each of their top 5 papers cited only 5 times!
• The h-index does not account for the number of authors of a paper. It gets counted as your paper even if you are one of 10 authors.
• The h-index does not account for the typical number of citations in different fields.
• The h-index means that scientists with a short career (fewer publications) are at a disadvantage, no matter how influential one paper might be
• The h-index does not consider the context of citations
• The h-index can be manipulated through self-citations

To compensate for these flaws (and more) a whole alphabet of indexes have been introduced to take into account things like very highly cited papers, early career researchers' impact, etc.

Next time we will look at some of these, and how they might be useful to researchers whose h-index is not so flash on its own.