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NAEP Technical DocumentationStratification of Public Schools for the 2011 Writing Computer-Based Assessment (WCBA)

Prior to stratification, the public school sampling frame was divided into grade-specific files, one each for eighth and twelfth grade. For each grade-specific frame file, separate implicit stratification schemes were used to sort schools into certainty primary sampling units (PSUs) and noncertainty PSUs. In all cases, the implicit stratification was achieved via a "serpentine sort."

For certainty PSUs, the schools were hierarchically sorted by

• census region,
• urbanization classification (urban-centric locale), and
• median household income in the zip code area where the school is located.

Schools in noncertainty PSUs were hierarchically sorted by

• PSU stratum,
• urbanization classification (urban-centric locale), and
• median household income in the zip code area where the school is located.

 

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