One issue that researchers acknowledge is the difficulty in comparing education levels.[11] The same number of years of schooling in two different countries may have very different educational content. Similarly, what is termed ‘primary school’ in different country may vary widely. Also, while extensive information for education in developed countries exists, data is only available for a small number of developing countries.[11] This brings into question to what extent the results can be generalized for all developing countries.[11] Additionally, while the pure economic benefits are relatively uncontroversial, there is some discrepancy over how to measure the social benefits, with some variability between studies.[5]