Abstract
Discrepancies in item difficulty and discrimination across different examination bodies introduced biases that affect the fairness and validity of assessment outcomes and decision. Therefore, this study examines psychometric properties of Polytomous Economics Items of Senior Secondary Certificate Examinations (SSCE) in South- West Nigeria. A descriptive survey design was adopted. The population comprised all senior secondary school students III that offer Economics in 2024/2025 academic session in South-west Nigeria. A sample of 1,620 students were selected using multistage sampling procedure. The research instruments used for the study was adopted 2023 SSCE essay items of Economics Paper conducted by WAEC. The instruments were validated by experts and 0.76 reliability coefficient was obtained. Data collected were analyzed through the generalized partial credit model (GPCM) using the WinGen Software, percentages and Analysis of Variance(ANOVA) at0.05 alpha level. The study found that while most items displayed functioning step difficulties, three items (%)showed non-sequential transitions. Four (%) items moderately discriminated between ability levels, while most items performed poorly in this regard. These findings question the psychometric quality of the 2023 Economics Paper II and highlight the need for regular test item evaluation. The study concludes that weak parameter invariance may undermine score fairness, stressing the importance of routine assessment reviews of SSCE essay items in Nigeria.