Statistical Significance and Effect Sizes of Differences among Research Universities at the Level of Nations and Worldwide based on the Leiden Rankings

One can use the Leiden Rankings for grouping research universities by considering universities which are not significantly different as a homogeneous set. Such groupings reduce the complexity of the rankings without losing information. We pursue this classification using both statistical significance and effect sizes of differences among 902 universities in 54 countries; we focus on the UK, Germany, and Brazil as national examples. Although the groupings remain largely the same using different statistical significance levels, the resulting classifications are uncorrelated with the ones based on effect sizes (Cramèr’s V < .3). Effect sizes for the differences between universities are small (w <.2). The results based on statistical-significance testing can be understood intuitively. However, the results based on effect sizes suggest a division between a North-Atlantic and an Asian-Pacific group. The more detailed analysis of universities at the country level suggests that distinctions between more than three groups of universities (high, middle, low) are not meaningful.