Over the 200 years of its existence a large amount of documentation – particularly case studies – has been published on the curative effects of homeopathic medicines. Nevertheless, more rigorous types of research in homeopathy are necessary to firmly establish its therapeutic value.
Observational studies are clinical research studies that follow research participants over time without changing their treatment. In these studies inferences are drawn or hypotheses tested through observational methods. They usually involve some form of systematic documentation of clinical practice, and are neither randomized nor controlled in design.
In experimental studies – also called clinical trials – participants are allocated to the different treatment options by a random process. The therapy under investigation is compared with a control group, which might be well-established treatment, non-treatment, different doses of the same treatment, sham or placebo treatment, full-scale treatment, minimal treatment or alternative treatment.
Treatment effects estimated by trials of randomized and non-randomized design can be similar in magnitude.