NAEP Technical DocumentationSchool Base Weights

			Substitute public schools for reading, mathematics, science (grade 12 only) Substitute private schools for reading, mathematics, science Substitute public schools for science HOT and ICT Substitute private schools for science HOT and ICT

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);
• sampling frame (new school frame or not); and
• assessment subject (science HOTs and science ICT samples involved the selection of geographic units known as primary sampling units (PSUs), but reading, mathematics, and science did not).

The overall selection probability of an originally selected school in a reading, mathematics, or science sample is equal to its probability of selection from the NAEP public or private school frame.

The overall selection probability of a school from the new school frame in a reading, mathematics, or science sample 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.

The overall probability of selection of an originally selected school in either the science HOT or science ICT assessment reflects two components:

• the probability of selection of the PSU; and  
• the probability of selection of the school within the selected PSU from the NAEP public/private school frame.

By design, none of the science HOTs or ICT samples include any schools from the new school frame.

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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