Investigating the psychometric properties of a screening instrument for young children is necessary to ascertain its quality and accuracy. In light of the important role culture plays on human beliefs and parenting styles, a newly translated and adapted test needs to be studied. Evaluating outcomes on a translated version of a test may reveal significant information related to cultural specifications as well as the common nature of child development. The current study examined psychometric properties of the 48-month interval of the Ages and Stages Questionnaires: Social-Emotional Second Edition (ASQ:SE-2) and its Traditional Chinese version (ASQ:SE-TC), using item response theory (IRT). Participants in the U.S. included 3,005 young children/parents dyads; 1,455 dyads were collected to represent a Taiwanese sample. A two-dimensional Rasch Partial Credit Model (2D-RPCM), which was determined to present a better fit than a unidimensional Rasch Partial Credit Model, was used to examine the item fit, item difficulty, reliability, and item information curves to evaluate the psychometric properties on the ASQ:SE and ASQ:SE-TC. Further, differential item functioning was conducted to examine whether items were functioning differently in the two population groups. Lastly, the differences between the distributions of children's latent traits on the continuum of social and emotional competencies for the U.S. and Taiwanese samples were investigated. Based on findings, the adequacy of psychometric properties is discussed, providing insight into the quality of particular items. Identified differences between the two populations are explored by reviewing literature regarding cultural comparisons of child-rearing practices, parenting styles, and cultural beliefs. Future directions for research include examining the cultural equivalence between translated and original versions of other ASQ:SE-2 intervals. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]