The Chemical Concepts Inventory (CCI) is a multiple-choice instrument designed to assess the alternate conceptions of students in high school or first-semester college chemistry. The instrument was published in 2002 along with an analysis of its data from a test population. This study supports the initial analysis and expands on the psychometric data available. The CCI was given to over 2500 students from four universities. Data were analyzed using classical test theory and Rasch model methods. The classical test theory analysis found the CCI to have acceptable internal consistency (Cronbach's alpha = 0.73, pretest, and 0.76, posttest) and good test-retest reproducibility (Pearson correlation = 0.79, posttest). Most items were found to have good difficulty and discrimination values; however, a few had values that may warrant further evaluation. The Rasch analysis showed that the instrument and the items nicely fit the Rasch model. The data showed good separation reliability and that the instrument overall is at an appropriate level for the population. However, several gaps were found along the range of item difficulties, leading to less accurate estimations of student abilities. Overall, the CCI was found to be suitable for the large-scale assessment of students' alternate conceptions. (Contains 4 tables and 2 figures.)