The underlying theory in a literature review is the theoretical framework or set of concepts that guides the analysis and interpretation of the reviewed literature. It provides the structural foundation for understanding the topic of research and serves as a lens through which the existing research is evaluated and synthesized. The literature review helps to establish the gaps, inconsistencies, or contradictions in previous studies and identifies the research questions or hypotheses to be addressed in the current study. The choice of underlying theory depends on the research field, topic, and research objectives. It could be a specific theory, a combination of theories, or a conceptual framework that contextualizes the research and aids in organizing and analyzing the literature.
