Abstract
This paper analyzes the temporal change in the number of references per paper and the citation age distribution, and their influence on the macroscopic Journal Impact Factor (JIF) in natural science field and its subfields. The target is limited to 4463 journals that are continuously indexed by Journal Citation Reports from 2001 to 2009, in order to eliminate the influence of journal replacement. In the whole natural science field, all-aged references per paper continuously increase, but the increase in 1- and 2-aged references per paper is slight, meaning that older-aged references mainly contribute to the increase in references per paper. The change in JIF in the natural science field was affected by both 1- and 2-aged references per paper and the paper-growth rate, stronger by the latter. All-aged references per paper increase in the every subfield, but 1- and 2-aged references per paper increase in some subfields and decrease in others. The difference in the changing rate of JIF among subfields is affected the most strongly by the changing rate of 1- and 2-aged references per paper, next by the changing rate of paper-growth rate. The proportion of inter-subfield citations dose not have a significant effect.
