What did I learn from that list?
To understand the list, we first need to know how scientific journals are ranked. Journals in different categories are ranked according to the impact factor. For example, the impact factor of a journal in 2009 is calculated as the number of times articles published in 2007 and 2008 were cited during 2009, divided by the total number of articles published by that journal in 2007 and 2008. Simply said, it reflects the average citations per article a journal receives.
There are many ways to boost the impact factor. Some journals reduce the number of original articles and increase the number of review articles, which are known to be cited more often. Journals affiliated to certain societies have particular advantage because they can publish guidelines. I have also encountered journals that would explicitly ask authors to cite their articles before the papers would be accepted.
Let’s for the time being ignore the differences among individual journals’ strategies. The list is enlightening.
Overall, the impact factors of most journals are on the rise. This does not necessarily mean that new papers are more important than old ones. Rather, the phenomenon can be explained by the rapid increase in the number of journals in each category and the number of researchers. In fact, journals whose impact factors did not increase significantly in the last decade almost invariably fell back in rank.
Secondly, there was little change in the ranking of top journals in each category. This is due to the submission pattern of researchers. It is natural for researchers to submit their best works to the top journals. The other journals could just receive less important works and even papers that have been rejected by top journals. Thus the difference between top journals and the other journals perpetuates.
Moreover, the increase in impact factor and number of citations did not distribute evenly among all journals. The increase was more in general journals than in highly specialized journals. Although specialized journals may enjoy good years when the field is rapidly advancing, the downturn can be equally harsh. On the other hand, general journals can easily turn to more promising fields when the environment changes. This, of course, should apply to other industries as well.