Abstract
The study investigated the item parameters of Biology multiple choice test items of the 2015 and 2016 National Examinations COUNCIL (NECO) Senior School Certificate Examination (SSCE). The study adopted the ex-post facto research design. The population for the study comprised the candidates that sat for Biology during the 2015 and 2016 NECO SSCE in Osun State. Asample of 1,457 and 2,875 candidates responses for 2015 and 2016 SSCE Biology test were selected using multistage sampling procedure. Data were collected from Information Technology Service (ITS) unit of NECO using a hard-disk drive. Data collected were coded and analysed using Multi-dimensional Item Response Theory (MIRT) package of R for statistical analysis. The results showed that the 2015 NECO Biology SSCE multiple choice test, four items were too difficult (average a = 2.23) while 13 of the items were too easy (with average a of 0.12). Findings on the item parameters of the 2016 NECO Biology SSCE multiple choice test showed that two items were too difficult (with average a = 15.98) while six of the items were too easy (average a =0.20). However, all the test items possessed acceptable degree of discrimination (with b ranging between 0.70 and 4.59). The study concluded that 2015 and 2016 NECO Biology multiple choice SSCE items was multidimensional. However, 2015 NECO Biology items had more easy items than 2016 NECO Biology items while both 2015 and 2016 Biology discriminate effectively and the guessing parameters is significant.