In Denmark, every hospital discharge is recorded centrally as well as detailed cancer diagnoses, causes and date of death, use of prescription medicine and more demographic information like number of siblings, children, income, education and so on.
This information is extracted yearly from the registries on all the participants. This globally unique feature eliminates loss-to follow-up, which can distort many epidemiological studies. Furthermore, it makes it manageable to follow this large number of participants with a limited budget.
By default, most projects involving the Copenhagen General Population Study as a cohort should encompass all available participants. The advantage of this approach in contrast to nested case-control studies is that the Copenhagen General Population Study will contain an ever increasing amount of information on all participants allowing for detailed studies of risk factor interactions and in substrata of the general population. Furthermore, disease-free participants of the Copenhagen General Population Study are very well suited to act as controls in case-control studies, where other research groups can provide cases.
So far, the main focus of studies using the Copenhagen General Population Study has been genetic epidemiology, but we have also been focusing on intermediary variables like blood pressure or triglycerides in the blood and their association with risk of disease. Also, combinatoric approaches like Mendelian Randomization studies have been very succesful in examining causality between intermediary variables and risk for diseases.