NAEP collects and reports academic achievement at the national level and, for certain assessments, at the state and district levels. NAEP selects schools by a stratified random sampling procedure; students in those schools are selected randomly. This is accomplished by creating a sampling frame using the Common Core of Data (CCD) and the Private School Survey (PSS). NAEP is then administered to a sample of students from this frame who represent the student population of the nation as a whole and of individual states and districts participating in the Trial Urban District Assessment (TUDA).
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NAEP assesses representative samples of students rather than the entire student population. The sample selection process utilizes a probability sample design. In this type of sample, each school and each student has a known probability of being selected. The probabilities are proportional to the estimated number of students in the grade assessed. Samples are selected according to a multistage design, with students drawn from within sampled public and private schools nationwide. Read details of assessment sample design in the technical documentation and see a diagram of sample selection for NAEP state assessments.
The Common Core of Data (CCD) file serves as the sampling frame for the selection of public schools in each state/jurisdiction. The CCD is a comprehensive list of operating public schools in each jurisdiction that is compiled each school year by the National Center for Education Statistics (NCES). The sample of students in districts participating in the Trial Urban District Assessment (TUDA) represents an augmentation of the sample of students selected as part of the state samples. All students at more local geographic sampling levels also make up part of the broader samples. For example, the TUDA samples are included as part of the corresponding state samples, just as the state samples are included as part of the national sample.
The Private School Survey (PSS) is a survey of all U.S. private schools carried out biennially by the Census Bureau under contract to NCES. The PSS served as the sampling frame for private schools. While state and district results are based on samples of public schools only, the national results are based on the combined samples of both public and private schools.
Because the schools and students that participated in the assessment represents only a portion of the larger population of interest, the assessment results are weighted to make appropriate inferences about the populations from the student, school, and district samples. Sampling weights are adjusted to account for the disproportionate representation of some groups in the selected sample. This includes oversampling of schools with high concentrations of students from certain racial/ethnic groups and the lower sampling rates of students who attend very small schools.
National samples include both public and nonpublic schools. For national-only NAEP assessments (e.g., long-term trend), sampling begins with primary sampling units (PSUs) from the U.S. Census Bureau, which are a merging of the nation’s 3,000 counties. PSUs are categorized based on geographical (e.g., census region and locale) and demographic factors (e.g., income level). Ten percent of these PSUs are selected using probability proportional to sample size, meaning that larger PSUs have a greater likelihood of selection, resulting in a sample of 95 to 100 PSUs. Sampling in certain NAEP assessments (i.e., reading and mathematics) has expanded to allow for state-level analysis. In these assessments public school data for the national sample is composed of the sum of the state samples.
In the 1990s, the NAEP program expanded the assessment to the 50 states, the District of Columbia, and the Department of Defense Education Activity (DoDEA). State samples include only public schools. In a NAEP state assessment year the entire state is treated as a sampling unit.
In 2002, the first NAEP Trial Urban District Assessment (TUDA) was conducted in six large urban districts. Currently there are 27 TUDA districts. Larger TUDA districts have somewhat larger sample sizes than others. All data collection for TUDA districts contributes to state results.
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Once a school has been selected for either a state or national assessment, students within the school are selected for each subject area based on grade (4, 8, or 12).
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Students seated next to each other do not take the same version of the assessment. For each subject, there are several different versions of booklets.
Individual students complete only a subset of NAEP items. A technique called Balanced Incomplete Block (BIB) spiraling is used in which groups of items are systematically arranged with other groups of items within test booklets to assure that the entire content domain for the subject is covered. And all items are completed by a representative sample of students, though individual students complete only a fraction of the items.
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subject and item selection.