In their guest talk, Dr. Silke Schneider and Verena Ortmanns pointed to the fact that the reliability of comparative studies is reliant on the cross-national comparability of the data that are being used. They focused on the highest level of education (coded using ISCED, International Standard Classification of Education) to evaluate the consistency of various surveys for a large number of countries, controlling for both within and between survey constancy. Results show that, unless surveys change measurement processes, the educational distribution is rather stable within a survey over time (more so in official than in academic surveys), but that there are big differences between surveys due to inconsistencies in the implementation of ISCED across surveys.