I am very grateful to professor Olli Miettinen, Mc Gill University, Montreal, Canada, who in his advanced courses in epidemiology in Finland in the 1990´ies gave us as post grade students, the inspiration to continue in epidemiology. He taught us - and he still is teaching - how to get a critical view on the medical learning, research and practice. For example his genius view of Diag-gnosis, Ethio-gnosis and Pro-gnosis is an important key to understand how the research, medical practice and health preventive acitivites are parts of the quality improvement in all types of life alike the ISO standards used in the industrial production. Among his many important contributions to the development of epidemiology, he made it understandable to us how the main different types of study design are inter related, especially how the ”case-control” study design should be understood as part of the cohort study design. So the design of the objectives, of the study populations and the domain is of crucial importance. See his books entitled: ”Up from clinical epidemiology” (2009) and ”Epidemiological Research: Terms and Concepts” (2011).