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Computation of Base Weights for the 2007 Assessment


School Base Weights

Student Base Weights

Every sampled school and student received a base weight equal to the reciprocal of its probability of selection. The details of how the school base weight was computed vary by whether the school was an original school (i.e., selected from either the public or private school frame), a new school, or a substitute school.

Computation of a student base weight reflects 

  • the student's overall probability of selection accounting for school and student sampling;
  • assignment to session type at the school- and student-level; and 
  • the student's assignment to the mathematics, reading, or writing assessment. 

Last updated 28 August 2009 (JL)

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