The authors recognize that “In general, it is difficult for global ranking systems to gather reliable per capita data at the national level, which may account for the strong emphasis on size-dependent, bibliometric indicators in global rankings” but they they fail to point out the strong limitations of the QS ranking by giving less than 20% of the weigth to bibliometric indicators. Other authors have also questioned the accuracy of the QS ranking. Aguillo et al. (2010) wrote that “The QS is based on a not large and not representative enough survey that means the results are biased towards certain countries”. And Safon (2013) wrote that “the majority of the received questionnaires come from English-speaking countries, clearly favoring their universities”. Aguillo, I. F., Bar-Ilan, J., Levene, M., & Ortega, J. L. (2010). Comparing university rankings. Scientometrics, 85(1), 243-256. Safón, V. (2013). What do global university rankings really measure? The search for the X factor and the X entity. Scientometrics, 97(2), 223-244.