RCTs

Randomized controlled trials (RCTs) are experimental studies in which participants are randomly assigned to receive an intervention or a comparator. They aim to assess the causal effect of interventions on predefined outcomes while limiting bias and confounding. RCTs are widely used in medicine, public health, psychology, and related fields.

Key features include randomization to balance confounders, a control group, and, when possible, blinding of participants, clinicians, and outcome assessors to reduce bias. Allocation concealment prevents foreknowledge of assignments. Analyses commonly follow intention-to-treat principles. Outcomes are specified in advance, with sample size calculated to achieve adequate power.

Common designs include parallel-group trials, crossover trials, and factorial trials. Cluster randomized trials assign groups rather than individuals. Pragmatic trials test effectiveness in real-world settings, while explanatory trials test efficacy under ideal conditions. Blinding levels range from single- to double- or triple-blind; some trials are open-label.

RCTs provide high internal validity but may have limited external validity if conditions differ from routine practice. Ethical considerations include informed consent and independent review; trials require safety monitoring. Limitations include cost, duration, and recruitment challenges. Reporting should follow predefined protocols and guidelines such as CONSORT to improve transparency.

The modern randomized trial emerged in the mid-20th century, with the 1948 streptomycin trial frequently cited as a landmark. Since then, RCTs have become central to evidence-based decision making across disciplines.