West Africa Examination Council (WAEC) and National Examination Council (NECO) are the two major examination bodies saddled with the responsibility of awarding Senior Secondary School Certificate in Nigeria. This study examined the comparability of the psychometric properties of the items constructed by the two examination bodies using Item Response Theory (IRT) approach. Three parameters (difficulty, discriminating and distrator Indices) logistic model was adopted for the study. The study employed descriptive research design of the survey type. The population for the study comprised all Senior Secondary School Students who enrolled for 2019 WAEC and NECO examinations in South West, Nigeria. The sample for the study consisted of 1,200 Senior Secondary School Students selected using multistage sampling procedure. The instruments for the study were objective items constructed by the examination bodies. The findings of the study showed that the difficulty and guessing indices of the mathematics items constructed by the two examination bodies are comparable while the discriminating powers not comparable. It is, therefore, recommended that certificates issued by WAEC and NECO could be used for same purposes without any discrimination since the items constructed by the examination bodies are of comparable standard in terms of their qualities.
Key words: Difficulty levels, discriminating powers, guessing indices, Item Response Theory (IRT), West Africa Examination Council (WAEC), National Examination Council (NECO).