Using an item-specific predictor to test the dimensionality of the orthographic choice task.

The orthographic choice (OC) task-requiring individuals to choose the correct spelling between a word and a pseudohomophone foil (e.g., goat vs. gote)-has been used as an outcome measure of orthographic learning and as a predictor of individual differences in word reading development. Some consider the OC task a measure of orthographic knowledge (e.g., Conrad, Harris, & Williams (Reading and Writing, 26(8), 1223-1239, 2013)), whereas others have suggested that the task measures a reader's familiarity with the word's orthographic representation and thus measures word reading skill (e.g., Castles & Nation, 2006). We examined this assertion by testing OC task performance of individuals ages 8 to 18 (J = 296) and their ability to read the OC target words (I = 80) in isolation using crossed random effects item-response models. Results reveal that response on the OC task is not fully determined by the ability of an individual to read the target word in isolation. Specifically, the probability of choosing the correct orthographic form when the word was pronounced incorrectly was .79; whereas it was .90 when the word was pronounced correctly. Measures of receptive spelling and phonemic awareness (person-characteristics) and word frequency and orthographic neighborhood size (item-characteristics) accounted for significant variance in orthographic choice after controlling for target item reading and other reading-related abilities. We interpret the results to suggest that the OC task taps both item-specific orthographic knowledge and more general orthographic knowledge.