We divide the research activities in three types that cannot be sharply delimited. The research can be done among sick people or among a group of healthy people. These types of research in populations corresponds also to the process of diagnostic,  treatment and control of effect that are used in the general medical practice to treat single patients. And it corresponds also very well to the activities that are planned and implemented to prevent diseases or injuries in healthy populations. 

Descriptive research is used to describe the status and the long-term trends of diseases, mortality and the risk factors. The research is used to point out the most serious and vulnerable parts of the population and to prioritize the intervention programs. Clinical descriptive studies are used to evaluate the precision of the diagnostic tools, for example the evaluation of the precision of tests for dementia or clinical tests for hypertension.

Causal research  or analytical research is used to identify the causal relations supposed to be major impeding or promoting factors for the health and safety. Most often done as cohort and case-control studies in the target populations. 

Experimental  or intervention studies are either clinical experiments that are used to test the effect of new treatments. The other type of experimental studies are used among to find the most effective type of prevention for example for hypertension.