A controlled trial is a type of scientific study in which participants are randomly assigned to either an experimental group or a control group. The goal of this design is to minimize the influence of other factors that could affect the results, such as differences between individuals or their backgrounds. In a controlled trial, the researchers measure the outcomes for both groups and compare them to determine if there are any significant differences in response to the intervention being tested. This type of study helps to establish cause-and-effect relationships and provides strong evidence about the effectiveness of an intervention or treatment.