Examining national citation impact by comparing developments in a fixed and a dynamic journal set

In order to examine potential effects of methodological choices influencing developments in relative citation scores for countries, a fixed journal set comprising of 3232 journals continuously indexed in the Web of Science from 1981 to 2014 is constructed. From this restricted set, a citation database depicting the citing relations between the journal publications is formed and relative citation scores based on full and fractional counting are calculated for the whole period. Previous longitudinal studies of citation impact show stable rankings between countries. To examine such findings coming from a dynamic set of journals for potential “database effects”, we compare them to our fixed set. We find that relative developments in impact scores, country profiles and rankings are both very stable and very similar within and between the two journal sets as well as counting methods. We do see a small “inflation factor” as citation scores generally are somewhat lower for high-performing countries in the fixed set compared to the dynamic set. Consequently, using an ever-decreasing set of journals compared to the dynamic set, we are still able to reproduce accurately the developments in impact scores and the rankings between the countries found in the dynamic set. Hence, potential effects of methodological choices seem to be of limited importance compared to the stability of citation networks