Real‐world evidence and observational studies: Methodological challenges in clinical research

The emergence of real-world evidence (RWE) has significantly broadened the scope of clinical research in internal medicine, providing insights that extend beyond the constraints of randomized controlled trials (RCTs). RWE is generated from real-world data (RWD)-information collected outside experimental settings, such as routine clinical practice. Observational studies, including cohort, case-control and cross-sectional designs, are fundamental to RWE generation, enabling the examination of patient outcomes, treatment patterns and disease epidemiology as they naturally occur. The expanded use of registries and electronic health records (EHRs) has revolutionized data collection, offering both depth and breadth for large-scale, longitudinal studies. However, drawing causal inferences from observational research presents substantial methodological challenges, as confounding and bias arising from non-randomized treatment allocation and unmeasured variables can distort results. Data quality issues-such as missing data, exposure and outcome misclassification, and inconsistent variable definitions-further complicate analysis. Advanced statistical techniques, including propensity score matching and instrumental variable analysis, have been developed to mitigate the limitations due to confounding, yet cannot fully substitute for randomization. Transparent reporting, pre-registration of protocols, and adherence to standardized guidelines (e.g. STROBE) are essential to enhance rigor and reproducibility. Despite their challenges, observational studies remain indispensable for addressing clinical questions that cannot be answered by RCTs, informing practice and guiding healthcare policy. Careful study design, rigorous analysis and transparent reporting are crucial for maximizing the reliability and impact of real-world evidence in internal medicine.