Study designs in clinical research

In nephrology research, both observational studies and randomized controlled trials (RCTs) are commonly applied. Clinicians using the evidence from epidemiological studies should be aware of the specific qualities and limitations of each study design. The purpose of the article is therefore to provide a brief overview of the range of study designs and to comment on the most important strengths and weaknesses of these designs. In general, RCTs are the optimal study design to study the effects of therapy or other interventions and to establish causality, although their use is limited by ethical and practical concerns. Conversely, observational study designs, including case reports, case series, cross-sectional studies, case-control studies and cohort studies, are usually more useful than RCTs for non-therapeutic research questions. In conclusion, both observational studies and RCTs fulfill a complementary and valuable role in nephrology.