[Visualization of period prevalence in dynamic populations: a teaching design and preliminary application]

There is a persistent inconsistency between the definition of period prevalence (PP) and its practical calculation, which poses a challenge in teaching epidemiology. This paper proposes a visual teaching design for a "three-tiered relationship diagram of disease duration, case numbers and population size within a dynamic population", based on a unified timeline. First, cases are classified into four categories according to the relationship between disease duration and the study period, with a clear distinction between new and pre-existing cases. Second, the person-time (area under the curve) interpretations of the integrals of real-time case counts, cumulative case counts, their maximum value, and population size over time are explained. Third, a theoretical PP formula based on the person-time ratio is established, from which two simplified formulas are derived. The relationships among the three formulas are clarified, and their application is demonstrated using examples of type 2 diabetes and influenza. Centered on the relational graph, this teaching design integrates conceptual analysis, formula derivation, and case validation. A small-scale pilot teaching session has shown preliminary effectiveness, and directions for future application and research are discussed.