PREVIC: An adaptive parent report measure of expressive vocabulary in children between 3 and 8 years of age.

Parent report measures have proven to be a valuable research tool for studying early language development. Caregivers are given a list of words and are asked which of them their child has already used. However, most available measures are not suited for children beyond infancy, come with substantial licensing costs or lack a clear psychometric foundation. Here, we present the PREVIC (Parent Report of Expressive Vocabulary in Children), an open-access, high-quality vocabulary checklist for German-speaking children between 3 and 8 years of age. The PREVIC was constructed leveraging the advantages of item response theory: we designed a large initial item pool of 379 words and collected data from 1190 caregivers of children between 3 and 8 years of age. Based on these data, we computed a range of fit indices for each item (word) and used an automated item selection algorithm to compile a final pool that contains items that (a) vary in difficulty and (b) fit the Rasch (one-parameter logistic) model. The resulting task is highly reliable and shows convergent validity. The IRT-based construction allowed us to design an adaptive version of the task that substantially reduces the task duration while retaining measurement precision. The task - including the adaptive version - was implemented as a website and is freely accessible online ( https://ccp-odc.eva.mpg.de/previc-demo/ ). The PREVIC fills an important gap in the toolkit of researchers interested in language development and provides an ideal starting point for developing converging measures in other languages.