What type of research design involves manipulation of an independent variable?

The correct choice involves an experimental design, which is characterized by the manipulation of an independent variable to assess its effects on a dependent variable. In this type of research, the researcher intentionally alters one factor while controlling for others to isolate the cause-and-effect relationship. This manipulation allows for the establishment of causal links, providing stronger evidence for hypotheses compared to other designs that may only observe or describe relationships without intervention.

In contrast, observational studies involve watching subjects in natural settings without intervention, which limits the ability to determine causality. Descriptive research primarily focuses on providing a detailed account of a phenomenon, often summarizing data without manipulating variables. Correlational studies investigate relationships between variables to see how they relate but do not involve manipulation, which means they cannot definitively establish cause and effect. Thus, experimental designs stand out as the most effective means of testing hypotheses about causal relationships due to their inherent structure of manipulation and control.