Lexile Word Frequency Profiles

This report describes the development of a new type of frequency measure for words that better reflects the developmental nature of word exposure. The relationship between word frequency and word knowledge has been well documented (Brysbaert, Buchmeier, Conrad, Jacobs, Bölte, & Böhl, 2011; Rudell, 1993). Indeed, word frequency is the operational measure of semantic difficulty in the equation powering the Lexile Analyzer® (Stenner, Horabin, Smith, & Smith, 1988; Stenner, Burdick, Sanford, & Burdick, 2007). However, the underlying theoretical explanation of why word frequency predicts word knowledge is exposure. Readers are exposed more often to more frequent words, and thus have greater knowledge of them (Klare, 1963). The connection between word frequency and word knowledge therefore is more meaningful if the word frequencies more accurately reflect the degree of exposure to a word for the average developing reader. Leveraging the power of the 1.4-billion-word MetaMetrics® corpus of texts intended for readers in U.S. K-12 schools, we developed the Lexile Word Frequency Profile, a set of frequency measures describing the developmental trajectory of a word’s occurrences along the Lexile scale. We demonstrate the meaningfulness and utility of Lexile Word Frequency Profiles by examining a few specific word profiles and using the profiles to predict other measures of word familiarity