Diagnosing students’ misconceptions in engineering education is a crucial task for designing targeted instructional interventions. This study presents a new approach to the development and validation of Four-Tier Diagnostic Test as an instructional tool for assessing engineering students’ conceptual understanding and misconceptions. The study aimed to evaluate the psychometric properties of the developed instrument and to identify the level of engineering students’ conceptual understanding and misconceptions in microwave engineering courses. A cohort of 141 undergraduate engineering students who took part in the course were administered with the developed 28-item Four-tier Diagnostic Test. Results of the study indicated that 24.7% of students demonstrated scientific knowledge, while 20.3% exhibited misconceptions. Regression analysis revealed a logarithmic relationship between students’ misconceptions and their overall performance, with misconceptions being present even among higher-performing students. Item response analysis using the mirt package showed that test items were effective in discriminating between students with different levels of conceptual understanding. While satisfactory KR-20 reliability coefficients for scientific knowledge (KR- 20=0.739 ) and misconceptions (KR- 20=0.749 ) were achieved respectively, the overall scale marginal conditional reliability (ρ > 0.907 ) indicates high precision of the instrument in measuring students’ conceptual attributes. This study contributes to the literature by demonstrating how multi-tiered diagnostic assessment coupled with advanced psychometric approaches can enhance the precision of educational diagnostics test. © 2013 IEEE.
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