Precision in the measurement of lexical expertise: the selection of optimal items for a spelling assessment.

Skilled adult readers vary in many skills related to visual word form processing such as phonological processing, vocabulary size, comprehension skill, and spelling skill (Kuperman & Van Dyke, 2011). Spelling skill in particular has received much attention because low- and high-skill spellers show different patterns of lexical processing as measured through eye movement behavior, reaction times, and word learning (Eskenazi et al., 2018; Veldre & Andrews, 2014). Researchers commonly use a spelling dictation task to measure lexical expertise; however, there is limited evidence for its psychometric properties and room for improvement in item selection (Andrews et al., 2020). The purpose of this study was to assess the precision of 110 words as measures of lexical expertise, to compare various subsets of words in a spelling dictation task, and to provide a set of words that more precisely measure lexical expertise. In Study 1, a spelling dictation task with 110 words was administered to 682 participants. In Study 2, that same task and measures of vocabulary and comprehension were administered to 786 participants. Results indicated that the set of 110 words contains many words that are imprecise measures of spelling skill. Through an iterative process of removing words with high error variance, a set of 20 words was selected that minimizes measurement error and demonstrates discriminant validity from vocabulary and comprehension ability. We recommend this set of words as a more precise measure of spelling skill, which will provide more power to detect moderating effects of lexical expertise on reading processes.