The growth of science and database coverage

Recently there has been huge growth in the number of articles displayed on the Web of Science (WoS), but it is unclear whether this is linked to a growth of science or simply additional coverage of already existing journals by the database provider. An analysis of the category of journals in the period of 2000-2008 shows that the number of basic journals covered by Web of Science (WoS) steadily decreased, whereas the number of new, recently established journals increased. A rising number of older journals is also covered. These developments imply a crescive number of articles, but a more significant effect is the enlargement of traditional, basic journals in terms of annual articles. All in all it becomes obvious that the data set is quite instable due to high fluctuation caused by the annual selection criteria, the impact factor. In any case, it is important to look at the structures at the level of specific fields in order to differentiate between real and artificial growth. Our findings suggest that even-though a growth of about 34 % can be measured in article numbers in the period of 2000-2008, 17 % of this growth stems from the inclusion of old journals that have been published for a longer time but were simply not included in the database so far.