The 2001 national main assessment surveys utilized the same original frame of schools as that used for the 2000 surveys. This frame was created by combining the 1997–1998 Common Core of Data (CCD) frame of public schools, and the 1997–1998 Private School Survey (PSS) file of nonpublic schools. More details about the construction of this frame can be found in the 2000 assessment sampling frame pages.
For the 2001 assessment, a differing set of primary sampling units (PSUs) was selected so that the final school frame was not identical to that used in the 2000 assessment. The population of eligible schools for each grade was restricted to the selected 94 PSUs. Any school having one or more of the eligible grades, and located within an appropriate PSU, was included in the sampling frame of schools (the list of schools from which the samples of schools were drawn) for a given sample. An independent sample of schools was selected for each of the grades.
For each school in each frame, the number of assessable students was provided by school officials. (See "Students Excluded from the 2001 National Main Assessment" for more information of those students deemed unable to participate in the assessment.) The CCD and PSS files give total enrollment, enrollment by grade, and the grade range for each school, thus providing the average enrollment per grade.
A school could appear on more than one grade-level frame. As a result, there is considerable overlap among the three grade-level frames.
Before selecting schools, high-minority public schools were identified for oversampling. The school was classified as high-minority if the percentage of Hispanic and Black students was reported to be greater than 10 percent (15 percent for grade 12) and if the number of Hispanics and Black students was reported to be at least 10 (15 for grade 12). Otherwise the school was classified as low-minority.