How is a texts Lexile measure determined?
Lexile measures are based on two well-established predictors of how difficult a text is to comprehend: semantic difficulty (word frequency) and syntactic complexity (sentence length). In order to establish the Lexile measure of a book or article, the text is split into 125-word slices. Each slice is compared to the nearly 600-million-word Lexile corpus-taken from a variety of sources and genres-and the words in each sentence are counted. These calculations are put into the Lexile equation. Then, each slice’s resulting Lexile measure is applied to the Rasch psychometric model to determine the Lexile measure for the entire text. For example, books like “Arthur and the Recess Rookie” (370L), “Arthur Goes to Camp” (380L) and “Arthur, Clean Your Room!” (370L) fall within the Lexile range of a typical American second grader. These books have shorter sentences and words appear frequently. Conversely, books in the “Harry Potter” series (which measure between 880L and 950L), “Little Women” (130
