A disadvantage is that unlike IQ-data collections, it does not include older people or more developing nations.[1] An advantage of using international student assessments instead of educational assessment is that "across countries and time, educational degrees are difficult to compare".[9] Compared to international student assessments, "literacy as the ability to read and write texts is a much too basic competence" and as a result "these three educational measures [literacy rate, years spent attending school, and highest achieved degree] usually show lower correlations compared to more complex ability measures".[9]