How many indicators do university rankings need?

The number of indicators used in international university rankings varies a lot. At one extreme we have the Russian Round University Rankings (RUR), which have 20 indicators. At the other, Nature Index and Reuters Top 100 Innovative Universities have just one.

In general, the more information provided by rankings the more helpful they are. If, however, the indicators produce very similar results then their value will be limited. The research and postgraduate teaching surveys in the THE world rankings and the RUR correlate so highly that they are in effect measuring the same thing.

There is probably an optimum number of indicators for a ranking, perhaps higher for general than for  research-only rankings, above which no further information is provided. 

A paper by Guleda Dogan of Hacettepe University, Ankara, looks at the indicators in three university rankings the Shanghai Academic Ranking of World Universities, the National Taiwan University Rankings and University Ranking by Academic Performance (URAP) and finds that they is a very high degree of internal  similarity:


"Results of the analyses show that the intra-indicators used in ARWU, NTU and URAP are highly similar and that they can be grouped according to their similarities. The authors also examined the effect of similar indicators on 2015 overall ranking lists for these three rankings. NTU and URAP are affected least from the omitted similar indicators, which means it is possible for these two rankings to create very similar overall ranking lists to the existing overall ranking using fewer indicators."