About the Assessment: Sample Design and Weighting
The schools and students participating in NAEP assessments are selected to be representative both nationally and for public schools at the state level. (In this report, only the results of the nation and the 11 selected states are reported.) While national and regional results reflect the performance of students in public schools, Bureau of Indian Education (BIE) schools, Department of Defense schools, and private schools, state-level results reflect the performance of public and BIE school students only. For comparison purposes within the state results section, the national sample is composed of public and BIE school students only.
The samples of AI/AN students participating in the 2007 NAEP reading and mathematics assessments represent augmentations of the sample of AI/AN students who would usually be selected by NAEP. Race/ethnicity information from official school records was used to identify AI/AN students during sampling. This allows more detailed reporting of performance for this group.
Prior to 2005, BIE schools were identified as part of the national sample, and the resulting number of participating schools was usually small, fewer than five per grade. In 2005, BIE schools were sampled as a part of each state sample, at the same rate as public schools in a given state. That means, roughly speaking, that a BIE student had the same probability of selection as a public school student in the same state. As a result, about 30 BIE schools were included per grade, thereby increasing the number of AI/AN students in the sample. In 2007, there were even larger samples of BIE schools than in 2005. About 120 BIE schools were included at grade 4 and 100 at grade 8.
Because the reporting of results at the state level was a goal of NIES Part I, schools in the following states were oversampled in 2007: Arizona, Minnesota, North Carolina, Oregon, and Washington. Samples from these schools were between 2 and 6 times higher than the schools with lower AI/AN populations.
Each school that participated in the assessment, and each student assessed, represents a portion of the population of interest. Results are weighted to make appropriate inferences between the student samples and the respective populations from which they are drawn.
Sampling weights compensate for the disproportionate representation of certain groups within the selected sample. This includes oversampling of schools with high concentrations of students from certain minority groups and lower sampling rates of students who attend very small nonpublic schools.
High density schools, those in which at least 25 percent of the students are AI/AN, were oversampled for NIES 2007 to support the reporting of results based on school density, which is the proportion of AI/AN students enrolled in a given school. Low density schools have less than 25 percent AI/AN students enrolled.
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