The present study examined the competing factor structures, validity, and reliability of the state and trait versions of the International Positive and Negative Affect Schedule – Short Form and the effect of the number of response categories on the scale qualities among Nigerians. Undergraduates (N-1510) completed a trait version of the scale with 5-point and 7-point response formats and a state version with a 7-point response format. Confirmatory factor analysis was employed alongside other techniques to gauge the psychometric properties of the scale. The obtained factor structures for the trait and state versions were in line with the theoretical assumptions of the scale and previous findings. A correlated two-factor model provided the best fit for the trait version, while an orthogonal two-factor model provided the best fit for the state version. The scale performed well with the 7-point response format, but it performed poorly with the 5-point response format, suggesting that the behaviour of the scale depends on the number of response categories. The findings, limitations of the study, and suggestions for further studies are discussed.