Clinical epidemiology is the science andmethod of studying the optimal decisions in clinical medicine, taking into consideration the epidemiologicalcharacteristics of the patient and his/her external clinicalenvironment, the disease involved, and factors andprocedures to which the patient is exposed in his/herclinical environment, specially clinical actions.Research should be a systematic process, organizedand objective, aimed to answer the question posed.Systematic means that the scientific method is applied,for that a hypothesis or work objective is formulated fromobservations or established knowledge about a topic, dataare collected following a pre-established design, and,once analyzed and interpreted, conclusions are obtainedwhich will modify or add new knowledge to the previous,and a new cycle starts again.Organization means that all members in the researchteam know perfectly what to do during the whole study,apply the same definitions and criteria to all participants, and act in identical way in front of any doubt. To achievethis, it is mandatory to write a protocol specifying alldetails related to the study.The meaning of the word objective is that conclusionsobtained are not based on subjective impressions but onfacts that have been observed, measured, and analyzed,and that any prejudice the study responsibles could haveis avoided during its interpretation.