A citation-based cross-disciplinary study on literature ageing: part II—diachronous aspects

In the first part of our study (Zhang and Glänzel in Scientometrics, 2017) we provided a view of the literature ageing based on a synchronous approach. Taking up the ideas by Egghe (Scientometrics 27(2):195–214, 1993) and Glänzel et al. (Scientometrics 109(3):2165–2179, 2016) we extend our study in the second part by applying a diachronous approach on the basis of citing literature. For this purpose we used the Prospective Price Index which was recently introduced by Glänzel et al. (Scientometrics 109(3):2165–2179, 2016). Finally, we compare the two aspects of literature ageing. In particular, we analyze the correlation between the share of recent references and the share of fast response, and found a generally positive correlation between both aspects at different levels of aggregation (subfields, major fields and the individual paper level). However, the consistence varies among different aggregations. For examples, on the level of subject fields, Chemistry, Biology, Neuroscience & Behavior are found with evidently better ranks by Prospective Price Index than Price Index, indicating their faster ageing process in the mirror of citations than references, while Engineering and Social sciences are found with the opposite ageing features. At the journal level, we observed a striking divergence between the reference and citation ageing patterns in some cases. Thus several journals proved ‘hard’ from the perspective of information sources (cited papers) but, at the same time, rather ‘soft’ in the light of information targets (citing papers).