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NAEP Assessment Sample Design → NAEP 2007 Sample Design → Sample Design for the 2007 State Assessment → Stratification of Schools for the 2007 State Assessment → Stratification Variables for the 2007 State Assessment

NAEP Technical DocumentationStratification Variables for the 2007 State Assessment

			Stratification by Urbanization Classification Stratification by Race/Ethnicity Classification Stratification by Achievement Data and Median Income Missing Stratification Variables

The stratification of public schools for the NAEP 2007 state assessment involved three dimensions within a jurisdiction. Public schools were stratified hierarchically by the following variables:

• urban classification, combined with whether or not the school is in a Trial Urban District Assessment (TUDA) district;

• race/ethnicity classification; and
• achievement score or median income of the ZIP Code area where the school is located.

The urbanization variable classifies schools by as many as eight types of location (e.g., central city, urban fringe of a city, town, rural area, etc.), which includes classification as to the size of the city or town and whether a rural area is in a metropolitan statistical area (MSA). This variable was nested within an indicator of whether the school was located in a TUDA district.

Student race/ethnicity status variables describe schools by the extent of race/ethnicity enrollment predominant in particular jurisdictions and represented in schools. Race/ethnicity classification is based on the Common Core of Data (CCD) race/ethnicity variables. The race/ethnicity cells are nested within the TUDA/urbanization classification (within each jurisdiction). 

The last stratification variable is achievement score or median household income. Achievement data were used if they were available for a particular jurisdiction and grade. If achievement data were not available, median household income from the 2000 census of the ZIP Code area where the school was located was used.

Missing values for stratification variables were imputed.

The implicit stratification in this three-fold hierarchical procedure was achieved via a "serpentine sort." This sort was accomplished by alternating between ascending and descending sort order on each variable successively through the sort hierarchy. Within this sorted list the schools were arranged in serpentine order by achievement data or median household income within each cell determined by the two higher classifications (urbanization/TUDA classification, race/ethnicity classification), with ascending order for achievement data/median household income used in every other cell, and descending order for achievement data/median household income used in the remaining cells, giving an ascending-descending-ascending-descending pattern. These urbanization/TUDA classification and race/ethnicity classification cells were also sorted in serpentine order. Within each urbanization/TUDA classification, race/ethnicity classification cells were sorted by ascending order for one urbanization/TUDA classification, followed by descending order for the next urbanization/TUDA classification, and so on.

Stratification variables sorted by serpentine sort: 2007

TUDA	Urbanicity	Race/ethnicity level	Achievement score
SOURCE: U.S. Department of Education, Institute of Education Sciences, National Center for Education Statistics, National Assessment of Educational Progress (NAEP), 2007.
Yes	1	High	20
			22
			27
			30
		Low	29
			26
			20
			18
	2	Low	15
			25
			27
			31
		High	35
			32
			30
			28
No	2	High	20
			22
			27
			30
		Low	29
			26
			20
			18
	1	Low	15
			25
			27
			31
		High	35
			32
			30
			28

Stratification differed for schools in the National Indian Education Study (NIES) oversample. These schools were implicitly stratified by the percentage of American Indian/Alaskan Native students within the school. 

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