NAEP Technical DocumentationSchool Base Weights for the 2010 Assessment

			Substitute public schools for the 2010 assessment Substitute private schools for the 2010 assessment

The school base weight for a sampled school is equal to the inverse of its overall probability of selection. The overall selection probability of a sampled school differs by

• type of sampled school (original or substitute); and
• sampling frame (new school frame or not).

The overall probability of selection of an originally selected school reflects two components:

• the probability of selection of the primary sampling unit (PSU); and  
• the probability of selection of the school within the selected PSU from either the NAEP public school frame or the private school frame.

The overall selection probability of a school from the new school frame is the product of two quantities:

• the probability of selection of the school's district into the new-school district sample; and  
• the probability of selection of the school into the new school sample.

Substitute schools are preassigned to original schools and take the place of original schools if they refuse to participate. For weighting purposes, they are treated as if they were the original schools that they replaced; so substitute schools are assigned the school base weight of the original schools.

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