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Computation of Base Weights


School Base Weights for Originally Selected Schools

School Base Weights for New Schools

School Base Weights for Substitute Schools

Student Base Weights


Every sampled school and student received a base weight equal to the reciprocal of its probability of selection. Base weights can vary because selection probabilities can vary. For example, in most states larger schools have a higher chance of selection than smaller schools; and consequently, selected smaller schools in these states have larger base weights than the selected larger schools. Computation of a school base weight varies by whether the school was an originally selected school (i.e., not a new or substitute school), a new school, or a substitute school.

Computation of a student base weight reflects its overall probability of selection accounting for school and student sampling and its assignment to the mathematics or reading assessment.

Last updated 06 November 2008 (RF)

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National Center for Education Statistics -
U.S. Department of Education