What is defined as a "randomized controlled trial"?

A randomized controlled trial (RCT) is characterized by its specific methodology, which includes the random assignment of participants to either an experimental group, which receives the treatment, or a control group, which does not. This design helps eliminate bias and provides a clear comparison to assess the effects of an intervention or treatment. The randomization process minimizes confounding variables, ensuring that differences in outcomes can be attributed to the intervention itself rather than other factors.

This robust design is crucial for establishing causal relationships and is a gold standard in clinical research. By contrast, the other options describe different types of study designs. Observational designs, prospective studies, and surveys do not involve the direct manipulation of an independent variable, which is essential for establishing cause-and-effect relationships inherent in RCTs.