Selecting the Samples for the 2005 Science AssessmentThe national results presented on this website are based on nationally representative probability samples of fourth-, eighth- and twelfth-grade students. At grades 4 and 8, the nationally representative sample in 2005 consisted of a combined sample of students assessed in each participating state, some students in states that did not participate in the state-level assessment, as well as students from nonpublic schools. This represents a change from previous assessments in which the national and state samples were independent. At grade 12, the sample was chosen using a stratified two-stage design that involved sampling students from selected schools (public and nonpublic) across the country. Each selected school that participated in the assessment and each student assessed represents a portion of the population of interest. Sampling weights are needed to make valid inferences from the student samples to the representative populations from which they were drawn. Sampling weights account for disproportionate representation of students from different states and for students who attend nonpublic schools. Sampling weights also account for lower sampling rates for very small schools and are used to adjust for school and student nonresponse. For the 2005 science assessment, accommodations for students with disabilities (SD) and English language learners (ELL) were permitted for the entire sample of students. This differs from the 1996 and 2000 science assessments, in which data were collected from samples of students where assessment accommodations were not permitted and from samples of students where accommodations were permitted. To learn more, read about the NAEP inclusion policy. View a summary of the national and state sample sizes and target populations for grades 4 and 8. View a summary of the district-level sample sizes and target populations for grades 4 and 8. View a summary of national and state student and school participation rates for the NAEP 2005 science assessment.
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