What distinguishes quasi-experimental designs from true experimental designs?

Quasi-experimental designs are characterized primarily by the absence of random assignment to treatment conditions. In these designs, researchers attempt to evaluate the effect of an independent variable on a dependent variable without the use of randomization. Because subjects are not randomly assigned, it can be challenging to make causal inferences, as the groups may differ in systematic ways that could affect the outcome.

True experimental designs, in contrast, utilize random assignment to ensure that participants have an equal chance of being assigned to any of the treatment conditions. This helps to reduce biases and confounding variables, allowing for clearer interpretations of causality.

The other options include aspects that do not accurately characterize the distinction between quasi-experimental and true experimental designs. For instance, focusing on qualitative data does not inherently define either design type. The manipulation of the independent variable is present in both design types, as both aim to assess the effects of such manipulation. Therefore, the essential feature that distinguishes quasi-experimental research from true experimental research is indeed the lack of random assignment.