There are different methods on how to measure the comparative aspect which differs from theoretical grounded studies intended to build or test complex models of educational systems to descriptive studies whose purpose is to monitor different features of educational systems, practices and outcomes. The purpose of theoretically oriented studies is mainly to examine relationships among variables and look for casual explanations. It is designed to examine links between school achievement and such characteristics as curricula, teaching methods, family expectations and funding levels. These highlight the level of differences between schools or classes as well as on differences between students as the unit of analysis. Belatedly, the intensification of international competition, spurred on by globalization, neo-liberalism and marketizing, has major implications for cross-national studies of educational achievement, for those engaged in or dealing with the powerful influence of national and international league tables, and for the theoretical frameworks that we employ in our analyses. If the funding of research is increasingly linked to commercial interests, for example, the potential for critical theory, or for alternative cultural perspectives to influence the construction of new knowledge, may be increasingly challenged. Questions of power and "whose knowledge counts?", in the process of development arise, perhaps, more strongly than ever before ( reference from my lecture notes).