Our ultimate goal is to develop a computerized test for assessing vocabulary in typically developing or language-delayed children. We expect this tool to have a market among both researchers and clinicians. The state of the art in rapid assessment of infant/toddler vocabulary is represented by the MacArthur Communicative Development Inventory (CDI), a validated paper-and-pencil instrument that queries parents about their children's knowledge of a standard set of common words. The culmination of over 20 years of research, the CDI was normed with a MacArthur Foundation grant, which we intend herein to leverage. We propose to elaborate methods developed under the PI's NSF funding to create a computerized vocabulary test based on the CDI, but boasting improved utility, reliability, and speed. In Phases I and II, we will (1) apply a new scoring methodology to improve reliability and broaden applicability to older children who are either typically developing or language-delayed, (2) apply adaptive computerized testing to increase reliability and speed, and (3) develop a prototype for a commercial-grade program that uses these methods. In Phase I, we will (1) develop algorithms for achieving these longer-term goals, (2) evaluate their efficiency via computer simulation, and (3) design the prototype. PROPOSED COMMERCIAL APPLICATION The last several years have seen the widespread adoption of the MacArthur Communicative Development Inventory as a research tool for evaluating infant/toddler vocabulary. The computerization of this tool, and the application of modern statistical methods, will render the instrument even easier-to-use. Its utility as a research tool will increase, and its enhanced potential for clinical use will expand the potential market.