Purpose: This paper introduces a series of short articles focusing on methodological tools in clinical research, and describes some of the relations existing between medical practice and clinical research.
State of the art and main points: The nature of the differences between statistical, epidemiological, and clinical uncertainty, and the lack of knowledge regarding relations between in vivo and in vitro phenomenon are explored. Also, notions of precision of numbers and validity of quantification are discussed and compared with the validity of narrative description of a pathological process, such as it is supposed to actually occur. PERSPECTIVES AND PROJETS: Intrinsic limitations of analytical and observational methods being explained, the usefulness of these same methods in the understanding of a disease or the evaluation of a therapy will be progressively described in more details.