Research as a source of evidence

The article presents the main sources of evidence that are an integral part of modern medical practice: primarily, controlled clinical studies. The concepts of research hypothesis, studied factors, and systematic and random errors are presented. A classification of errors is presented, and the design of their main types is described. The issues of the methodological level of planning, conducting, evaluating the results of the study, and their presentation in peer-reviewed medical publications are discussed. Particular attention is paid to the problems of external and internal validit y of the study and statistical and clinical significance of the results.