NAEP Technical DocumentationComputation of Base Weights for the 2011 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. Computation of a school base weight varies by

• type of sampled school (original or substitute);
• sampling frame (new school frame or not); and
• assessment subject (writing [WCBA] samples involved the selection of geographic units known as primary sampling units [PSUs], but reading, mathematics, and science did not).

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 reading, mathematics, science, or writing (WCBA) assessment. 

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