ABSTRACT
Clinicians and healthcare decision-makers conduct their clinical practice based on the results of clinical trials. However, some health problems remain unresolved; in such cases, further research is required. To ensure reliable research results, it is important to understand the study design and conduct well-designed clinical trials. Many study designs can be chosen within the two broad categories of observational and interventional. Clinical studies have a variety of designs, including case series, case-control, cross-sectional, and prospective and retrospective cohort studies. Well-designed clinical studies can clarify important differences between treatment options and provide data on long-term drug efficacy and safety. Interpreting the results of clinical trials can be difficult because weaknesses in research design, data collection methods, analytic methods, and reporting can compromise their value and usefulness. However, although randomized controlled trials are limited owing to ethical and practical issues, they are optimal for investigating the effects of therapy and establishing causality. Here we present an overview of different clinical research designs and review their advantages and limitations.