Conceptual and procedural knowledge retention in data visualization: a longitudinal study of doctoral learning and instructional design implications

Abstract Developing durable methodological capabilities is a central challenge in doctoral education. This study examined how doctoral students retain conceptual understanding and procedural execution in data visualization following formal instruction. Using a rubric-based assessment with verified inter-rater reliability, performance was evaluated at three time points: immediately after training, six months later, and twelve months later. Linear mixed-effects models captured longitudinal changes while accounting for individual variability. The results revealed significant declines in both dimensions, with sharper decay observed for procedural, tool-dependent execution. These findings suggest that conceptual understanding is relatively more resilient over time, whereas procedural fluency appears to depend more strongly on continued opportunities for practice and feedback. The study indicates that short-term methodological courses alone may be insufficient to ensure enduring competence. More broadly, the findings have implications for how doctoral education might better support the sustained development of data-visualization competence and highlight the need for further research on the learning environments and experiences that shape long-term retention. By linking cognitive theories of learning and forgetting with contemporary doctoral-training frameworks, this research contributes to understanding how methodological capabilities are retained, differentiated, and potentially strengthened through continued scholarly engagement.