Defining and Measuring the Undefinable: A Methodological Systematic Review of Student Engagement Operationalization in Hybrid Higher Education Research (2019-2025)

The widespread adoption of hybrid learning models in higher education following the COVID-19 pandemic has intensified longstanding challenges in defining and measuring student engagement. This methodological systematic review examines how student engagement has been conceptualized and operationalized in hybrid higher education research published between 2019 and 2025. Following PRISMA 2020 guidelines, we screened 1,867 records across five databases (ERIC, Scopus, Web of Science, PsycINFO, ProQuest), resulting in 66 included studies. Results reveal that while Fredricks et al.'s (2004) tripartite framework (behavioral, 84.8%; cognitive, 75.8%; emotional, 74.2%) remains dominant, significant methodological concerns persist. Critically, 65.2% of studies employed custom-developed or adapted scales rather than validated instruments, and only 19.7% used established measures. Misalignment between conceptual definitions and measurement approaches was prevalent, particularly for cognitive and agentic engagement dimensions. Social (12.1%) and agentic (7.6%) engagement remain underexplored despite their theoretical relevance to hybrid contexts. Geographically, research concentrates in Asia (50.0%) and North America (27.3%), limiting generalizability. The review identifies urgent needs for: (a) validated, hybrid-specific engagement instruments; (b) clearer alignment between theoretical frameworks and measurement approaches; (c) greater attention to emerging dimensions including social and agentic engagement; and (d) improved reporting of hybrid learning model specifications. We provide methodological recommendations to enhance construct validity, cross-study comparability, and cumulative knowledge building in this rapidly expanding field.