What differentiates a randomized controlled trial from a quasi-experimental design?

The key difference between a randomized controlled trial (RCT) and a quasi-experimental design lies in the presence of randomization. In a randomized controlled trial, participants are assigned to different groups (usually a treatment group and a control group) through a randomization process, which helps eliminate biases and ensures that any effects observed can be attributed to the intervention rather than other factors. This random allocation is crucial for ensuring that the groups are comparable at the start of the study.

In contrast, in a quasi-experimental design, randomization is not implemented. This means that the assignment of participants to groups is done based on criteria other than random selection, such as convenience of access or specific characteristics. As a result, while quasi-experimental designs can still provide useful insights, they are generally considered to have a higher potential for biases and confounding variables, which can affect the internal validity of the findings.

This absence of randomization in quasi-experimental designs is what distinctly sets these two types of studies apart. Understanding this fundamental difference is essential for evaluating the strength of the evidence generated by different research methodologies.