I would like to summarize the three types of studies we have covered in this lecture.  The goal of the cross-sectional study is a better understanding of the disease and risk factors that are associated with the disease.  The retrospective study is good to get an estimation of the potential risk factors and usually these relationships are confirmed by the prospective studies.  Therefore, the retrospective study is less valid than the prospective method.  The results from these  studies have been utilized for diabetes prevention, control, intervention, education and management.