NAEP Assessment Sample Design → NAEP 2011 Sample Design → Sample Design for the 2011 National Assessment → 2011 Writing Computer-Based Assessment (WCBA) → Selection of Primary Sampling Units for the 2011 WCBA and MCBS Assessments

NAEP Technical DocumentationSelection of Primary Sampling Units for the 2011 WCBA and MCBS Assessments

			PSU Generation: Metropolitan Statistical Areas PSU Generation: Certainty PSUs PSU Generation: Non-Metropolitan Statistical Areas PSU Frame: Stratification Final PSU Sample

For the writing computer-based assessment (WCBA) and mathematics computer-based study (MCBS), a sample of 105 primary sampling units (PSUs) was drawn from a frame of PSUs based on current Census information. 

After the PSU frame was created, 29 certainty PSUs (those with measures of size large enough that it is efficient to take them with probability of selection equal to 1) were identified and set aside. 

Stratification of the noncertainty PSUs (the remaining PSUs with probabilities of selection strictly less than 1) was carried out after analysis of Census 2000 data and NAEP 2000 achievement scores identified the stratification variables. This analysis identified the set of PSU-level, Census-based variables that had as much association with NAEP assessment scores as possible. The intent was that the results of this analysis and stratification would be used for multiple design years and subject matter.  The results were used previously in 2006, 2008, 2009, and 2010.  Periodically, this analysis and stratification will be conducted according to the availability of Census data and key assessment scores. Measures of size and probabilities of selection were defined for each PSU, and a stratified systematic sample of PSUs was drawn. For WCBA and MCBS, 76 noncertainty PSUs were selected.  

The PSUs on the frame satisfied the following criteria:

• The PSU sampling frame included all U.S. states and the District of Columbia, but excluded the U.S. territories and Puerto Rico;

• PSUs consisted of one county or contiguous multiple counties;

• Metropolitan Statistical Areas (MSAs) were designated as separate PSUs even with their large size, as they were sufficiently compact in terms of their travel costs (due to higher levels of transportation infrastructure);

• PSUs did not cross Census region boundaries;

• PSUs did not cross state boundaries, in general;

• Non-MSA PSUs in the Northeast and South Census regions had a minimum population of 15,000 youths (age 0 to 17 inclusive), and in the Midwest and West Census regions had a minimum population of 10,000 youths, in general, according to the 2003 U.S. Census Bureau's Population Estimates Program; and

• Non-MSA PSUs were to be of minimum size (defined in terms of maximum distance between points—a rough proxy for travel time) while still satisfying the minimum population constraints.

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