Which of the following is a secondary research methodology?

A secondary research methodology involves analyzing existing data that has already been collected and published by others, rather than collecting new data firsthand. A literature review fits this definition perfectly, as it involves synthesizing and evaluating previously published studies, articles, or reports to draw conclusions about the examined topic or area of research.

In this context, the other options involve primary research methodologies. Experimental research involves designing and conducting experiments to collect new data. Qualitative interviews require researchers to gather data directly from participants through questions and discussions, representing another form of primary data collection. Observational studies also entail the gathering of firsthand data based on observing subjects in their natural environment. Thus, the literature review stands out as the correct answer, aligning with the principles of secondary research.