Which type of study is classified as an experimental study?

The classification of a study as experimental is based on its design and the manipulation of variables to establish cause-and-effect relationships. In this context, a meta-analysis, while being a systematic review that aggregates data from multiple studies, does not involve direct experimentation or manipulation of variables by researchers.

The correct answer is thus a study that involves direct intervention, where researchers actively modify one or more variables and observe the outcomes in a controlled setting. Whereas a meta-analysis synthesizes existing study data and does not itself engage in experimental intervention, experimental studies typically include randomized controlled trials where participants are assigned to different groups to assess the effects of a treatment.

Therefore, understanding the different study designs can clarify their purposes: experimental studies test hypotheses through direct manipulation, while meta-analyses provide insights based on the outcomes of previously conducted studies without direct experimentation.