Southgate, V., Arnold, H., and Johnson, S. (1981). Extending Beginning Reading. London: Heinemann Educational Books.
Stenner, A.J. (1996). Measuring reading comprehension with the Lexile Framework. Durham, NC: Metametrics, Inc.
Ujiie, J. and Krashen, S. (1996). Comic book reading, reading enjoyment, and pleasure reading among middle class and chapter I middle school students. Reading Improvement, 33,1: 51-54.