Citations have become a standard feature of global university rankings, although they are measured in very different ways. Since 2003 the Shanghai Academic Ranking of World Universities has used the list of highly cited researchers published by Thomson Reuters (TR), who have now prepared a new list of about 3,500 names to supplement the old one which has 7,000 plus.
The new list got off to a bad a start in 2013 because the preliminary list was based on a faulty procedure and because of problems with the assigning of papers to fields or subfields. This led to ARWU having to repeat the 2012 scores for their highly cited researchers indicator in their 2013 rankings.
The list contains a number of researchers who appear more than once. Just looking at the number of Harvard researchers for a few minutes, I have noticed that David M Sabatini, primary affiliation MIT with secondary affiliations at Broad Institute Harvard and MIT, is listed for Biology and Biochemistry and also for Molecular Biology and Genetics.
Eric S Lander, primary affiliations with Broad Institute Harvard and MIT and secondary affiliations with MIT and Harvard, is listed three times for Biology and Biochemistry, Clinical Medicine and Molecular Biology and Genetics.
Frank B Hu, primary affiliation with Harvard and secondary affiliation with King Abdulaziz University, Saudi Arabia, is listed under Agricultural Sciences, Clinical Medicine and Molecular Biology and Genetics.
This no doubt represents the reality of scientific research in which a single researcher might well excel in two or more closely related fields but if ARWU are just going to count the number of researchers in the new list there will be distortions if some are counted more than once.
The new list refers to achievements over the period 2002-12. Unlike the old list, which just counted the number of citations, the new one is based on normalisation by field -- 21 in this case -- and by year of publication. In other words, it is not the number of citations that matters but the numbers in relation to the world average for field and year of citation.
TR acknowledge that there is a problem resulting from the growing number of massively cited, multi-authored papers and reviews, especially in the subfields of Particle and High-Energy Physics. To deal with this issue they have excluded from the analysis papers in Physics with more than thirty institutional addresses.
I do not know if TR are planning on doing this for their data for the Times Higher Education World University Rankings. If they are, places like Panjab University are in for a nasty shock.
Another noticeable thing about the new lists is the large number of secondary affiliations. In many cases the joint affiliations seem quite legitimate. For example, there are many researchers in subjects such as Biology and Biochemistry with affiliation to an Ivy League school and a nearby hospital or research institute. On the other hand, King Abdulaziz University in Jeddah has 150 secondary affiliations. Whether Thomson Reuters or ARWU will be able to determine that these represent a genuine association is questionable.
The publication of the new lists is further evidence that citations can be used to measure very different things. It would be unwise for any ranking organisation to use only one citations based indicator or only one database.