"In principle, medical research is classified into primary and secondary research. While secondary research summarizes available studies in the form of reviews and meta-analyses, the actual studies are performed in primary research. Three main areas are distinguished: basic medical research, clinical research, and epidemiological research." (www.aerzteblatt.de/pdf.asp?id=64227, 01.08.19)
1. Epidemiology (Population Research) is
"The study of how and why diseases occur in groups of people (populations). Scientists working in this field are called epidemiologists. They look for patterns and trends in illness to work out why certain diseases, such as cancer, occur in some people but not in others. ...
[2. Basic Research (Laboratory Research) is]
Scientists conduct laboratory experiments with the building blocks of disease to try to understand how a disease works. They study cells, proteins and DNA from humans and animals, or disease-causing agents such as chemicals, bacteria and viruses. Scientists also study and develop new drugs and treatments in the laboratory. ...
[3. Clinical Research (Patient Research) is]
Research conducted on people to better understand, diagnose, prevent and treat diseases. It is usually carried out in a clinical setting such as a hospital or outpatient clinic ..."