Clinical Epidemiology

The aim of clinical epidemiology is to select and systematise reliable results from different diagnostic and treatment methods, and to develop and apply methods of clinical observation that allow fair conclusions to be drawn, avoiding the influence of systematic and random errors. In order to avoid systematic errors, the specifics of patient selection are taken into account. Intervening factors are assessed. Attention to measurement methods is mandatory. Random errors cannot be avoided, but the extent of their influence can be quantified by statistical methods. A central tenet of clinical epidemiology is that every clinical decision must be based on rigorously proven scientific evidence. According to the principles of evidence-based medicine, only methods proven to be effective by rationally organised objective comparative studies should be used in the diagnosis, treatment and prevention of diseases.

There are certain requirements that must be met if the results are to be considered as a guide for action. These are: correct study design and a mathematically sound method of randomisation; clearly defined and observed inclusion and exclusion criteria; correct choice of criteria for disease outcome and treatment efficacy; and correct use of statistical methods for data processing. A distinction is made between experimental (controlled, with deliberate intervention) and observational studies. In experimental, the researcher can control or manipulate the factor whose influence on the outcome of the disease is to be studied and analysed. In the absence of this, the research is referred to as observational. The latter may be retrospective or prospective, which are preferable because they are more accurate. In terms of organisation, observational studies are divided into one-stage and longitudinal studies. The first is a case or series of cases, the second is a case-control study, a cohort study.

A prerequisite for a well-designed experimental trial is randomisation, a procedure that ensures that patients are randomly allocated to the experimental and control groups. Studies may be single-centre or multicentre, in which more than one institution is included in the trial. Randomised trials may be open-label or "blinded" (masked). In order to implement the results of evidence-based trials, it is necessary to clearly describe the categories of patients whose treatment was studied in order to compare them with other patients who need to be treated. Indirect measures of treatment effectiveness include positive changes in any of the indicators under investigation. Direct measures include recovery, reduced mortality and complications, shorter hospital stays, improved quality of life.

In summary, randomised controlled (prospective) double- or triple-blind trials are regarded as the gold standard in international practice. The materials of these trials and the meta-analysis conducted on their basis should be used in medical practice as a source of the most reliable information. Organising, conducting and evaluating evidence-based clinical trials is a complex and costly process, and it is essential that data already available are used in general practice.