Observational study

An observational study , an observational study, is a clinical study in which a researcher collects data by simply observing events in their natural course without actively interfering with them. The opposite of observational research is experiment .

An observational study can be either “transverse” (simultaneous) or “longitudinal” (lasting over time). A one-stage study, in which a single measurement of indicators and determination of the relationship between them occurs, are the most unreliable from the point of view of evidence-based medicine . Comparison of indicators obtained at different points in time during a longitudinal study reduces the likelihood of error. The most reliable data can be obtained during an observational study in a specially formed group. The choice of observation time is carried out depending on the duration of the observed process and is not limited by anything ^[1] .

Observational studies are less reliable than controlled trials , which compare outcomes in the intervention group and the control group ^[1] .

The main types of observational studies are cohort and case-control studies ^[2] :

• In a cohort study, an isolated group of people ( cohort ) is observed for some time. The condition of patients in different subgroups of this cohort, those who have been or have not been (or have been subjected to varying degrees) to treatment with the studied drug, are compared. In a prospective cohort study, a research plan is first drawn up and the order of data collection and processing is determined, then cohorts are compiled, research is conducted and the data obtained is analyzed. In a retrospective cohort study, the cohort is selected from archival records and the health status of patients is monitored from the moment the patient is monitored to the present.

• In the case-control study, people with a certain disease are compared with people from the same population who do not suffer from the disease in order to identify the relationship between the clinical outcome and the previous exposure to certain riskogenic factors.

A drawback of observational studies is the high likelihood of a systematic error. However, they may be the researcher's only choice in cases where other types of research are not possible for ethical or economic reasons ^[1] .