NAEP Technical DocumentationStratification Variables for the 2011 State Assessment


			Stratification by Urbanicity Classification Stratification by Race/ethnicity Classification Stratification by Achievement Data and Median Income Missing Stratification Variables

The implicit stratification of public schools for the NAEP 2011 state assessments involved three dimensions:

urbanicity classification (urban-centric locale);
race/ethnicity classification; and
achievement level or median income.

The urbanicity stratum is the top-level implicit stratification variable and is assigned within each explicit stratum. It is derived from the NCES urban-centric locale variable and classifies schools based on location (city, suburb, town, rural) and proximity to urbanized areas. It has 12 possible values.

The race/ethnicity stratum classifies schools by the relative magnitude of non-Hispanic White, non-Hispanic Black, Hispanic, Asian and Pacific Islander, and American Indian and Alaska Native enrollments represented in schools. The source of the race/ethnicity data is the Common Core of Data (CCD). The race/ethnicity stratum is the second-level variable in the stratification hierarchy and is nested within the urbanicity stratum.

The last stratification dimension is a classification of schools based on either achievement data or median household income. For most states, it is based on achievement data. However, not all states provide achievement data. In these cases, median household income is used instead. Median income comes from the 2000 Census and it corresponds to the zip code area where the school is located.

Missing values for stratification variables were imputed.

The implicit stratification in this three-fold hierarchical procedure was achieved via a "serpentine sort" within a given explicit stratum. 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 stratification variables (urbanicity and race/ethnicity classifications), 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. Schools in these urbanicity and race/ethnicity classification cells were also sorted in serpentine order. Within each urbanicity and race/ethnicity classification cells, schools were sorted in ascending order within one urbanicity stratum, by descending order within the next urbanicity stratum, and so on. The following table shows an oversimplified example to illustrate the ascending-descending-ascending-descending pattern of the serpentine sort.

Stratification variables sorted by serpentine sort: 2011
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), 2011 State Assessment.
Yes	Large City	High minority	20
			22
			27
			30
		Low minority	29
			26
			20
			18
	Mid-size City	Low minority	15
			25
			27
			31
		High minority	35
			32
			30
			28
No	Mid-size City	High minority	20
			22
			27
			30
		Low minority	29
			26
			20
			18
	Large City	Low minority	15
			25
			27
			31
		High minority	35
			32
			30
			28

The third dimension of stratification differed for schools in the National Indian Education Study (NIES) oversample. These schools were implicitly stratified by the percentage American Indian/Alaskan Native students within the school instead of achievement scores or median household income.

Last updated 12 July 2012 (JL)

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