We say a (randomized) controlled clinical trial for a specific study design. Now my question is, what is controlled refering to?
Different things come up to my mind:
- Controlled in the sense that the design and the process of the study is fixed before the study begins, so before the data is genereated i.e. before the patients receive the treatment
- controlled in the sense that in a controlled clinical trial you always have a control group, in opposite to most observational studies, where there not necessarily a control group (in a case-control-study you do have a control group and this is also a observational study)
- controlled in the sense that you control for unobserved confounders