The study found that Lexile was successful at matching students to texts with respect to reading accuracy (93%), but not at matching readers to texts that they could read at an acceptable rate: "Without support, either in the form of fluency modeling or repeated reading, these texts would be too difficult for these students to read productively on their own." In 2002, the Lexile framework was evaluated by Dale Carlson. The independent consultant found that the Lexile framework had a "well-delineated theoretical foundation." Both Carlson and Mesmer have remarked on the positive and unique characteristic of having both the student and text on the same scale. In 2001, the National Center for Educational Statistics (NCES) formally reviewed Lexile measures. The report acknowledged the science behind Lexile measures: “The panel affirmed the value of both sentence length and word frequency as overall measures of semantic and syntactic complexity...” Additionally, according to one panel member, the Lexile Framework appears “…exceptional in the psychometric care with which it has been developed; the extent of its formal validation with different populations of texts, tests, and children; in its automation; and in its developers’ continual quest to improve it.” However, the report also identified a number of issues and the different authors identified a range of concerns, such as the exclusion of factors such as reader knowledge, motivation and interest: "The notion of purpose in reading is excluded in the Lexile Framework. This is a serious oversight because of the dramatic effects that purpose can have on reading." Stephen Krashen, educational researcher in language acquisition and professor emeritus at the University of Southern California, raised serious concerns with the Lexile rating system in his article, "The Lexile Framework: Unnecessary and Potentially Harmful." Krashen argues that a reading difficulty rating system limits children's choices and steers them away from reading books in which they may be interested. Furthermore, like most reading formulas, the formula used to determine a book's Lexile level can often lead to a flawed rating. For example, "The Library Mouse", by Daniel Kirk, is a 32-page children's picture book rated by Amazon.com as "for ages 4-8" and has a Lexile score of 830. However, Stephenie Meyer's 498-page, young adult novel "Twilight" only garners a Lexile score of 720. Similarly, Beverly Cleary's "Ramona Quimby, Age 8", has a Lexile score of 860, while Michael Crichton's "Jurassic Park" only has a score of 710.