Background Randomized placebo-controlled trials are considered to be the gold standard in clinical research and have the highest importance in the hierarchical system of evidence-based medicine. However, from the viewpoint of decision makers, due to lower external validity, practical results of efficacy research are often not in line with the huge investments made over decades. Method We conducted a narrative review. With a special focus on homeopathy, we give an overview on cohort, comparative cohort, case-control and cross-sectional study designs and explain guidelines and tools that help to improve the quality of observational studies, such as the STROBE Statement, RECORD, GRACE and ENCePP Guide. Results Within the conventional medical research field, two types of arguments have been employed in favor of observational studies. First, observational studies allow for a more generalizable and robust estimation of effects in clinical practice, and if cohorts are large enough, there is no over-estimation of effect sizes, as is often feared. We argue that observational research is needed to balance the current over-emphasis on internal validity at the expense of external validity. Thus, observational research can be considered an important research tool to describe “real-world” care settings and can assist with the design and inform the results of randomised controlled trails. Conclusions We present recommendations for designing, conducting and reporting observational studies in homeopathy and provide recommendations to complement the STROBE Statement for homeopathic observational studies.

Case reports have been of central importance to the development of homeopathy over the past 200 years. With a special focus on homeopathy, we give an overview on guidelines and tools that may help to improve the quality of case reports. Reporting guidelines such as CARE (Case Report), HOM-CASE (Homeopathic Clinical Case Reports), and the WissHom Documentation Standard help to improve the quality of reporting and strengthen the scientific value of a case report. Additional scientific tools such as prospective outcome assessment, prognostic factor research, cognition-based medicine, and the Modified Naranjo Criteria for Homeopathy (MONARCH) score may be helpful in improving case documentation and evaluation.

The N-of-1 trial design offers important new investigative possibilities in homeopathy and should be explored as a means to optimise individualised health care or investigate effectiveness of the homeopathic intervention compared with placebo in individual subjects.

Due to the low quality, the small number and the heterogeneity of studies, the current data preclude a decisive conclusion about the comparative effectiveness of IHT. Generalisability of findings is limited by the variable external validity identified overall; the most pragmatic study attitude was associated with RCTs of adjunctive IHT. Future OTP-controlled trials in homeopathy should aim, as far as possible, to promote both internal validity and external validity.

Background Clinical observational studies are an important methodological approach in human and veterinary research, examining and describing treatment experience with good external validity. There are currently few observational studies in the field of homeopathic veterinary medicine. Aim The aim of the study was to develop recommendations for designing, conducting and reporting observational studies in homeopathic veterinary medicine. Materials and Methods A literature review was performed using various search strategies for identifying guidelines and checklist tools relevant for observational studies, veterinary research and homeopathy. Useful guidelines were selected. Prior recommendations for designing and conducting observational studies in human homeopathic medicine were supplemented with recommendations for homeopathic veterinary medicine that were evaluated by an expert panel. Results The veterinary extension of the Strengthening the Reporting of Observational Studies in Epidemiology – Veterinary (STROBE-Vet) statement was identified as a useful tool to improve the reporting quality of observational studies, and it has been supplemented here with additional recommendations that are applicable to homeopathy. STROBE-Vet is complemented in the literature by several reports, checklists and guidelines on veterinary medicine in general, such as the Checklist for One Health Epidemiological Reporting of Evidence (COHERE) and the Animal Health Surveillance Reporting Guidelines (AHSURED). Identified items that related to laboratory animal research were excluded as non-relevant to our study. Conclusion Clinical observational studies are an important methodological approach, having currently unrealized potential in the field of homeopathic veterinary medicine. With relatively minor adjustments, the practical guidelines and checklists available to researchers in designing, conducting and reporting observational studies in human homeopathic medicine have been adapted for homeopathic veterinary medicine, for which high quality can be assured by implementing recommendations such as those in STROBE-Vet. With the emergence of the One Health concept, the COHERE checklist can be viewed with growing significance.