Citation statistics, ecological journals, and ecology

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Citation statistics of ecological journals have been the focus of a number of recent postings on ECOLOG-L. These postings in many cases reflect a lack of understanding of how these statistics are calculated, what they mean, and why they are dangerous to us as individuals and to our field if used incorrectly. Recall that these statistics are used by libraries to decide which journals to purchase, by departments as a tool in tenure decisions, and even by national governments in deciding how to allocate research funds.

The most popular statistic is the "impact factor". The definition of "IF" is the number of current-year citations to articles in the journal by other journals included in Science Citation Index during the two years prior to the current year, divided by the number of articles in the journal in the same period.

Observe the following:

1. Citations to the same journal are not counted, which results in small fields and specialty journals getting low scores.

2. Only the most recent two years count; citations to older papers are not included. This has the advantage that new journals are not at a disadvantage. HOWEVER, it does mean that journals in fields with a focus on description of diversity and which must build on a large foundation of observations accumulated over many years are at a decided disadvantage. Thus, fields like ecology, systematics, geology, geography, and anthropology will cite older articles and will receive lower citation statistics than fields like molecular biology and physics. For comparisons of journals in the more descriptive fields, the half-life statistics for the journals should also be considered.

3. The literature has become so large that many scholars take the easy way out and cite review articles in preference to primary literature. Note that 3 of the top 6 ecology journals (as recently reported on ECOLOG-L) are review journals.

4. There is no correction for length of articles, and long articles are likely to contain more information (results) and are, consequently, more likely to be cited than short articles. Note that 2 of the top 6 ecology journals have the word "Monographs" in the title.

The way ecologists publish is different from the way scientists in some other fields publish, and this is reflected in citation statistics. Tables published in the recent National Academy evaluation of graduate programs are revealing. Below I show for the top 25% of graduate programs in each of 5 fields the mean number of publications and the mean number of citations per program faculty member.

   Field                           Publs    Citations

   Ecology, Evolution & Behavior    7.03      36.15
   Molecular & General Genetics    12.67     214.34
   Neurosciences                   11.97     136.51
   Cell & Developmental Biology    11.79     153.76
   Biochemistry & Molecular Bio.   11.87     158.66
Note that ecologists publish fewer papers. This does not mean that they do less research. Ecologists tend to publish a smaller number of longer papers and take more time to do the research per publication. As most of you realize, field work takes a long time.

Note also that ecologists collect fewer citations per faculty member, in large part because they publish fewer papers, but also because much of ecology is specific to the organism or system and thus not broadly generalizable. We do not focus all our work on Yeast, flies, mice, and a small number of other model systems. Moreover, an ecologist's citation record is likely to build slowly because the half-lives of his ro her papers is relatively long compared to other fields.

In conclusion, be careful how you use citation statistics and, even more importantly, understand them well enough that you can defend your discipline and colleagues in your discipline when citation statistics are used as tools for evaluation.

Robert K. Peet
Editor-in-Chief
Ecology & Ecological Monographs

The "top" 12 ecology journals as presented on ECOLOG-L based on Impact factor.


Ecological Monographs
Annual Review of Ecology and Systematics
Trends in Ecology and Evolution
Wildlife Monographs
American Naturalist
Advances in Ecological Research
Ecology
Journal of Animal Ecology
Evolution
Evolutionary Ecology
Oikos
Journal of Ecology
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 Robert K. Peet                      Phone:    919-962-6942
 Department of Biology, CB#3280        Fax:    919-962-6930
 University of North Carolina        Email:    robert_peet@unc.edu
 Chapel Hill, NC  27599-3280  USA
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