<![CDATA[This study employed a quantitative descriptive approach using a four-tier diagnostic test combined with Rasch modeling to examine students’ conceptual understanding of vibration, wave, sound, and light. These topics were selected because they are structurally connected in the junior high school physics curriculum and require students to relate definitions, physical quantities, representations, and scientific reasoning. Misunderstanding in one topic may affect students’ comprehension of related concepts. The study involved 221 second-year junior high school students from Cianjur, West Java, Indonesia. Data were collected using a 20-item four-tier diagnostic instrument. Rasch analysis was used to examine measurement quality through unidimensionality, item fit, reliability, and the Wright map. The results showed acceptable person reliability of 0.79 and high item reliability of 0.94, indicating adequate consistency in estimating student ability and item difficulty. Findings revealed that students mainly showed partial understanding, followed by misconceptions, while complete understanding remained limited. The most difficult concepts were related to frequency, amplitude, sound propagation, perceived sound frequency, and the distinction between mechanical and electromagnetic waves. The Wright map showed heterogeneous student ability and varied item difficulty on a common logit scale. This study contributes by showing how four-tier diagnostic assessment supported by Rasch modeling can provide specific diagnostic evidence for identifying conceptual gaps and guiding targeted physics instruction]]>
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