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Computation of Base Weights for the 2008 LTT 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) or a substitute school.

Computation of a student base weight reflects 

  • the student's overall probability of selection accounting for school and student sampling; and
  • the student's assignment to the reading or mathematics assessment. 

Last updated 21 December 2009 (JL)
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National Center for Education Statistics -
U.S. Department of Education