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A Hirsch-type index for journals

Source: Web of Science, accessed September 16, 2005Re: the h index.1 We suggest that a h-type index – equal to h if you have published h papers, each of which has at least h citations – would be a useful supplement to journal impact factors. First, it is robust and therefore insensitive to an accidental excess of uncited papers and also to one or several outstandingly highly cited papers. Second, it combines the effect of "quantity" (number of publications) and "quality" (citation ra

By | November 21, 2005

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Source: Web of Science, accessed September 16, 2005

Re: the h index.1 We suggest that a h-type index – equal to h if you have published h papers, each of which has at least h citations – would be a useful supplement to journal impact factors. First, it is robust and therefore insensitive to an accidental excess of uncited papers and also to one or several outstandingly highly cited papers. Second, it combines the effect of "quantity" (number of publications) and "quality" (citation rate) in a rather specific, balanced way that should reduce the apparent "overrating" of some small review journals.

The journal h-index would not be calculated for a "lifetime contribution," as suggested by Hirsch for individual scientists, but for a definite period – in the simplest case for a single year. Fortunately, the Web of Science database offers a very simple way to determine the annual h-index of a journal without the need for any off-line data processing. Retrieving all source items of a given journal from a given year and sorting them by the number of times cited, it is easy to find the highest rank number which is still lower than the corresponding times cited value. This is exactly the h-index of the journal for the given year.

We chose 2001 as a starting year, and looked for citations until the time of accessing the database on September 16, 2005. We used the Journal Citation Reports 2001 for comparative impact factor data. The list of the ten journals with the highest h-index for their 2001 papers is given in Table 1. Conspicuously, the first and second ranked journals of the 2001 impact factor list – the Annual Review of Immunology and the Annual Review of Biochemistry – are missing from the table. Since they published 24 and 23 papers, respectively, in 2001, they had no chance to compete with the chart toppers, because the h-index cannot be larger than the number of papers it is based on.

This in no way meant to belittle the significance of these journals, but does stress the different dimensions emphasized by the two indicators. Not surprisingly, the majority of the journals in the table below are from the biomedical field, a fact that underlines the necessity of discipline-specific evaluation of this indicator, as well. Nevertheless, beyond the two multidisciplinary journals leading the list, there are two physics journals (Physical Review Letters and Astrophysical Journal) and one from chemistry (Journal of the American Chemical Society) in the top 20. These three journals – the most prestigious in their fields – ranked outside the top 100 by impact factor, which demonstrates the slightly more balanced character of this indicator.

On the other hand, the highest journal h-index in mathematics is 12, for the Journal of Functional Analysis, which, with a multiple tie somewhere around the 1500th position is certainly meaningless if the real "impact" of the journal is sought. Hirsch's h-type indices will certainly challenge scientometrists and other number crunchers for a while.

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