Observational Studies in Neurosurgery: Structure, Functioning, and Uses

INTRODUCTION: Although randomized interventional studies are the gold standard of clinical study designs, they are not always feasible or necessary. In such cases, observational studies can bring insights into critical questions while minimizing harm and cost. There are numerous observational study designs, each with strengths and demerits. Unfortunately, it is not uncommon for observational study designs to be poorly designed or reported. In this article, the authors discuss similarities and differences between observational study designs, their application, and tenets of good use and proper reporting focusing on neurosurgery. METHODS: The authors illustrated neurosurgical case scenarios to describe case reports, case series, and cohort, cross-sectional, and case-control studies. The study design definitions and applications are taken from seminal research methodology readings and updated observational study reporting guidelines. RESULTS: The authors have given a succinct account of the structure, functioning, and uses of common observational study designs in Neurosurgery. Specifically, they discussed the concepts of study direction, temporal sequence, advantages, and disadvantages. Also, they highlighted the differences between case reports and case series; case series and descriptive cohort studies; and cohort and case-control studies. Also, they discussed their impacts on internal validity, external validity, and relevance. CONCLUSION: This paper disambiguates widely held misconceptions on the different observational study designs. In addition, it uses case-based scenarios to facilitate comprehension and relevance to the academic neurosurgery audience.