Study types

A clinical study is a research study using human subjects to evaluate biomedical or health-related outcomes. On the English version of this website, clinical studies are divided up into the subsidiary groups clinical trials, observational studies, diagnostic studies and qualitative studies.

Clinical trials

Clinical trials are sometimes called intervention studies or experimental studies. Within the framework of a clinical trial, study participants are exposed to some kind of intervention, for example a medicine, a medical device, a diet or a surgical method according to a previously agreed protocol. The purpose is to investigate or confirm the safety or effect of the therapy or method.

In a controlled clinical trial, the new therapy or method is compared with a control consisting of an established therapy or method, placebo or no measure at all. In a randomised controlled trial, the study participants are allocated randomly between the treatment groups.

Observational studies

Observational studies are sometimes called non-intervention studies, or non-experimental studies. No active measure is taken, instead the study participants are observed during current circumstances. Observational studies may, for example, consist of ecological or epidemiological investigations, cross-section investigations, cohort investigations or case-control investigations.

Diagnostic studies

Diagnostic studies investigate diagnostic tests aimed at identifying persons with a disease or health problem. The outcome of a diagnostic study has no immediate, direct value for the study participants. The concepts of sensitivity and specificity are often used to describe the reliability of a diagnostic test.

Qualitative studies

In qualitative studies, the research question is answered by interpreting events and development of categories or models that describe a phenomenon or a context, rather than by numbers and statistics. The most common way of working is through comprehensive interviews.