Evidence-based medicine combines principles and methods. Due to the action of these principles and methods of solution, instructions and strategies in medicine are based on current evidence on the effectiveness of various forms of treatment and medical services in general. In relation to medicines, evidence-based medicine relies heavily on information obtained during the assessment of benefits and risks (effectiveness and safety).
The concept of evidence-based medicine appeared in the 1950s. Up to this point, doctors had made decisions mainly based on their education, clinical experience, and reading scientific periodicals. However, studies have shown that decisions about medical treatment varied significantly from one medical professional to another. A base was formed for the introduction of systematic methods for collecting, evaluating and organizing scientific research data, which became the beginning of evidence-based medicine. The emergence of evidence-based medicine has been recognized by doctors, pharmaceutical companies, regulatory authorities, and the public.
The decision maker needs to draw on their own patient experience combined with the best supporting evidence from controlled research and scientific development. It is important to combine clinical experience and controlled research in the decision-making process. In the absence of clinical experience, the risk associated with a particular treatment may result in undesirable effects.

One approach to evidence-based medicine involves a 5-step model:

1. forming a clinically relevant query (the doctor's search for information to make a correct diagnosis),
2. searching for the best supporting data (the doctor's search for supporting data to support the information found in stage 1),
3. evaluating the quality of supporting data (ensuring high quality and reliability by the doctor),
4. forming a medical decision based on supporting data (making an informed decision by the patient and the doctor about treatment based on stages 1-3),
5. evaluation of the process (evaluation by the doctor and the patient of the achieved result and appropriate adjustment of treatment decisions, if necessary).

In the above example, the choice of a doctor is consistent with both the principles of evidence-based medicine and patient feedback. The decision made by the doctor implies a conscious, open and informed use of the best supporting evidence at the current time, including the patient's experience, to choose the best possible way of medical care for this patient.
Patient participation in the decision-making process is essential for developing new treatment principles. Such participation involves reading and understanding treatment information and consciously following recommendations, working with clinical specialists to evaluate and select the best treatment options, as well as providing feedback on the results obtained. Patients can actively participate in the creation of supporting data at any level.

The collected information is classified according to the level of supporting evidence it contains to assess its quality. The pyramid in the figure below illustrates the different levels of supporting evidence and their ranking.

This is evidence based on the opinions of a panel of experts and aimed at shaping general medical practice.

A case series is a descriptive study of a small group of people. It typically serves as a supplement or appendix to a clinical case report. A clinical case report is a detailed account of the symptoms, signs, diagnosis, treatment, and follow-up of a single patient.

A case-control study is an observational retrospective study (with a review of historical data) in which patients suffering from a disease are compared with patients who do not have this disease. Cases such as lung cancer are usually studied using the case-control method. For this purpose, a group of smokers (the group under the influence) and a group of non-smokers (the group not under the influence) are recruited, who are monitored for a certain period of time. Then the difference in the incidence of lung cancer is documented, which allows us to consider a variable (an independent variable, in this case, smoking). as the cause of the dependent variable (in this case, lung cancer).
In this example, a statistically significant increase in lung cancer cases in the smoking group compared with the non-smoking group is considered as confirmation of a causal relationship between smoking and the occurrence of lung cancer.

The modern definition of a cohort in a clinical trial is группа individuals with certain characteristics who are being monitored to identify health-related consequences.
The Framingham Heart Disease Study is an example of a cohort study conducted to find an answer to a question in the field of epidemiology. The Framingham study began in 1948 and continues to this day. The aim of the study is to study the impact of a number of factors on the incidence of heart disease. The question facing researchers is whether factors such as high blood pressure, overweight, diabetes, physical activity, and other factors are associated with the development of heart disease. To study each of the impact factors (for example, smoking)recruited by researchers группа smoking people (группа under the influence) and группа non-smokers (группа not under the influence). The groups are then monitored for a certain period of time. Then, at the end of the follow-up period, the difference in the incidence of heart disease in these groups is documented. The groups are compared in terms of many other variables, such as
economic status (for example, education, income, and occupation),
and health status (for example, the presence of other diseases).
This means that a variable (the independent variable — in this case, smoking) can be isolated as the cause of the dependent variable (in this case, lung cancer).
In this example статистически A significant increase in the incidence of heart disease in the smoking group compared with the non-smoking group is considered as confirmation of the causal relationship between smoking and the occurrence of heart disease. The results discovered during the Framingham study over the years convincingly prove that cardiovascular diseases are largely the result of measurable and correctable risk factors, and that a person can control the health of their cardiac system if they carefully monitor their diet and lifestyle and refrain from consuming refined fats and cholesterol. smoking, reduces weight or begins to lead an active lifestyle, regulates stress levels and blood pressure. It is mainly thanks to the Framingham study that we now have a clear understanding of the association of certain risk factors with heart disease.
Another example of a cohort study that has been conducted for many years is the National Child Development Study (NCDS), the most studied of all British cohort studies of newborns. The largest study on women is the Nurses Health Study. It began in 1976, and the number of escorted persons is more than 120,000 people. According to this study, many diseases and outcomes were analyzed.

Clinical trials are called randomized if a randomization method is used to assign participants to different treatment groups. This means that treatment groups are filled randomly using a formal system, and for each participant there is вероятность get into each of the directions being explored.

Мета-анализ — is a systematic, statistically based examination of data that compares and combines results from different studies, aiming to identify patterns, inconsistencies, and other relationships across multiple studies. Мета-анализ It can serve as a confirmation for a more convincing conclusion compared to any individual study, but it is necessary to keep in mind the disadvantages associated with systematic errors due to the preferred publication of positive research results.

The study of results is a broad umbrella concept that does not have a permanent definition. The results study examines the final results of medical care, in other words, the effect of the process of providing medical services on the health and well-being of patients. In other words, clinical outcome studies aim to monitor, understand, and optimize the impact of medical treatment on a specific patient or a specific group. Such studies describe scientific research that is related to the effectiveness of health measures and medical services, that is, the results obtained through such services.
Attention is often focused on the person suffering from the disease — in other words, on the clinical конечные точки (overall outcomes) that are most relevant for that patient or group of patients. Such endpoints may be качество жизни or the degree of pain. However, outcome studies can also focus on the effectiveness of health care delivery, with measurement parameters being эффективность затрат, health status and severity of the disease (the impact of health problems on a person).
The difference between evidence-based medicine and outcome research is the focus on different issues. While the main objective of evidence-based medicine is to provide optimal medical care to the patient in accordance with clinical evidence and experience, research on the results is primarily aimed at determining the endpoints. In a clinical outcome study, these points usually correspond to clinically relevant endpoints.
In outcome studies, relevant endpoints often become symptoms or parameters measuring functional abilities and care needs — something that the patient receiving treatment considers important. For example, a patient suffering from an infection who has been injected with penicillin may pay more attention to the fact that he does not have a fever and his general condition has improved than to the effect of penicillin on the actual level of infection. In this case, the symptoms and how he feels are considered as a direct assessment of his state of health — and these are конечные точки,which are the focus of attention when conducting a study of the results. The patient is also likely to be interested in the possible side effects associated with penicillin, as well as the cost of treatment. In the case of other diseases, such as cancer, an important clinical outcome relevant to the patient will be риск fatal outcome.
If the study is lengthy in time, when studying the research results, the following methods can be used: «суррогатные конечные точки». Суррогатная конечная точка involves the use of a biomarker to measure an outcome, acting as a surrogate for a clinical endpoint measuring эффективность. Рассмотрим клиническое исследование, in which the effect of penicillin is tested by reducing the amount of one type of protein (C-reactive protein), which is always present in the blood. The amount of this protein in the blood of a healthy person is very small, but with an acute infection it increases rapidly. Thus, measuring the level of C-reactive protein in the blood is an indirect way to determine the presence of infection in the body, therefore, in this case, the protein serves as a "biomarker" of infection.. Биомаркер — this is a measurable indicator of the state of the disease. This parameter is also correlated with the risk of developing or progressing the disease or with how the prescribed treatment will affect the disease. A blood sample is taken daily from the patient for analysis to measure the amount of the biomarker in the blood.
It should be emphasized that in order to use a surrogate endpoint for the purpose of control and supervision, the token must be confirmed or verified in advance. It is necessary to demonstrate that changes with the biomarker are correlated (consistent) with the clinical outcome in the case of a specific disease and the effect of treatment.