16.2.1 Scopus versus ISI
The difference in citation records between ISI versus Scopus varies hugely by discipline. For the academics working in the Sciences, Scopus generally finds fewer citations than ISI, with the exception of our Computer Scientist. For the academics working in the Social Sciences and Humanities Scopus generally finds more citations than ISI, with the exception of the Cinema Studies academic.
As is readily apparent from Figure 1, the pattern of reduced citation scores for the Scientists is most pronounced for the Pharmacologist who sees his citations reduced by more than 50%. His most cited article has 919 citations in ISI, but only 248 in Scopus. The simple reason for this is that Scopus only includes citations from 1996 onwards. In fact, Scopus and ISI provide a virtually identical number of citations for this article from 1996 onwards. As this particular academic has been publishing for more than 40 years, his citation record in Scopus is very incomplete.
The Cell Biologist, Mathematician and Physicist also experience drops of around 25%, even though they have only been publishing for around 25 years. Again, this is caused by the fact that Scopus does not include citations before 1996 and all of these academics published some articles before this date. Comparison of individual articles published after 1995 shows virtually identical citation records in ISI and Scopus. If anything, Scopus tends to show a marginally higher number of citations for these articles.
Figure 1: Number of citations for ISI and Scopus General Search: Science disciplines
In contrast, our Computer Scientist sees his citations increase by 43% in Scopus. There are several reasons for this. First, although this academic has been publishing for 31 years, many of his most cited articles were published after 1995 and hence Scopus restricted data coverage is not a problem. Second, the Computer Scientists benefits from the broader data coverage of Scopus in his field. Whilst ISI lists only 62 articles for him, Scopus lists around 100 articles. This difference did not occur for the other academics working in the Sciences.
Social Sciences and Humanities
For four of our academics working in the Social Sciences and Humanities (Business, Education and Linguistics), Scopus finds more citations than ISI. As shown in Figure 2, this pattern is pronounced for the Business academic who sees her citations increase by 77%. As she only started publishing in 1995, the lack of citation coverage before 1996 is not a problem. Moreover, Scopus lists an additional 10 articles for her in journals that are not ISI-listed, but are included in the Scopus database. This includes her most highly cited article. In addition, because Scopus has a wider journal coverage in Business than ISI, citations for all her articles tend to be at least 10%, but sometimes 50% higher than citations in ISI.
A similar pattern is found for the academic working in Education. He even sees his citations increase by 90%, largely because Scopus lists more of the journals he has published in, but also because Scopus citations to articles listed in both databases are 20-100% higher than ISI citations. The Linguist and the Political Scientist only show a modest increase by 18-20% as for them better journal coverage in Scopus is counterbalanced by a reduction in pre-1996 citations. However, for the journal articles that are listed in both sources, Scopus generally provides 20-80% more citations than ISI. Hence journal coverage in four of the Social Sciences and Humanities fields seems much broader in Scopus.
Figure 2: Citations for ISI and Scopus General Search: Social Science and Humanities disciplines
The Cinema Studies academic is worst off when using the Scopus database as nearly all of her journal publications date from before 1996, and the journals she has published in do not have pre-1996 coverage in Scopus. However, the only article by this academic that is included in Scopus has more citations than in ISI.
Comparing ISI and Scopus as a source for citations provides mixed results. In general, Scopus provides a higher citation count than ISI, both in the Sciences and in the Social Sciences and Humanities. In the Sciences, this increase in only marginal (except for Computer Science), whilst in the Social Sciences and Humanities, this increase is substantial.
Scopus appears to have a much broader journal coverage for the Social Sciences and Humanities than ISI and hence provides a fairer comparison. Whilst in ISI academics working in the Sciences have on average 17.5 times as many citations as the academics working in the Social Sciences and Humanities, in Scopus this difference is reduced to 7.5 times.
However, for the time being Scopus is hindered by its lack of coverage before 1996. This means that for most established academics in the Sciences, Scopus will lead to lower lifetime citation counts than ISI. In the Social Sciences and Humanities, a substantially increased citation count is likely for academics who have published the majority of their highly cited work after 1996.