Fuzzy data definitions distort fair comparability of universities in university rankings: results from Italy and Belgium on the Times Higher Education Ranking

World university rankings have had an impact on academic competition worldwide. The comparability of ranking results depends on how data is collected within each university. When data concepts are interpreted differently, data variety is introduced and ranking results cannot be used in a meaningful manner. In this case study, the effect of semantic harmonisation of the data concepts of the Times Higher Education World University Ranking is evaluated. Based on two independent initiatives, in Italy and in Belgium, the data and results of this ranking before and after interuniversity harmonisation of data collection are compared. This study demonstrates that, despite the data definitions provided by the ranking organisation, the data concepts ‘academic staff’ and ‘students’ are interpreted differently within each university. These differences can affect how universities are positioned relative to each other in ranking tables. A profound level of semantic harmonisation is then required to ensure semantically comparable data.