The Progress in International Reading Literacy Study (PIRLS) of 2001 is a large international comparative study of the reading literacy of young students. The student population for the U.S. 2001 PIRLS was the set of all fourth-graders in the United States, corresponding to the grade in which the highest proportion of nine-year-olds are enrolled. Because the response rate from the original sample was below 85 percent, NCES investigated the potential magnitude of nonresponse bias at the school level. The methodology and results of this investigation are presented in this report.
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