The SASS sample is a stratified probability-proportionate-to-size (PPS) sample. With the exception of BIE schools, all schools underwent multiple levels of stratification.3 The sample was allocated so that national-, regional-, and state-level elementary, secondary, and combined public school estimates could be made. The sample was allocated to each state by grade range (elementary, secondary, and combined) and school type (traditional public, public charter, BIE-funded, and schools with high American Indian enrollment). For a full description of the allocation procedure, see the Documentation for the 2007-08 Schools and Staffing Survey (Tourkin et al. forthcoming). Within each stratum, all non- BIE schools were systematically selected using a PPS algorithm. The measure of size used for the schools was the square root of the number of full-time-equivalent teachers reported or imputed for each school during the sampling frame creation. Any school with a measure of size greater than the sampling interval (the inverse of the rate at which the sample is selected) was included in the sample with certainty and thus automatically excluded from the probability sampling operation. (For a more detailed explanation of PPS sampling, consult Sampling Techniques [Cochran 1977].) These sampling procedures resulted in a total public school sample of about 9,800 public schools (including both traditional public and public charter schools) and 180 BIE schools in the 2007-08 SASS.
Private schools. The 2007-08 SASS private school frame was based on the 2005-06 Private School Universe Survey (PSS).4 The PSS is designed to generate biennial data on the total number of private schools, students, and teachers and to build a universe of private schools in the 50 states and the District of Columbia to serve as a sampling frame of private schools for NCES sample surveys, such as SASS. Prior to each PSS collection, NCES updates the list of schools to be included in the PSS by collecting membership lists from private school associations and religious denominations, as well as private school lists from state education departments. This list-frame update is intended to improve coverage of new private schools and private schools previously not included in the PSS. Since the list-frame update for the 2007-08 PSS preceded the SASS frame building, the SASS private school sample frame was augmented with the private schools discovered during the PSS list-frame update. The SASS private school frame also includes schools in the 2005-06 PSS area frame. This area frame includes schools that were overlooked in the list-building operation. In a sample of 124 geographical areas (out of 2,062), local field staff used such resources as local telephone directories, local resource guides, etc., to identify schools. The resultant lists of schools were matched to the PSS list frame, and any school that was not part of the list frame was added as an area frame school.
During the creation of the SASS private school sampling frame, schools with kindergarten as the highest grade level were deleted from the frame. Also, private school records that were missing information necessary for the SASS school sample selection were amended. For example, the school grade range was needed to stratify SASS schools during the private school sampling process. If the data on school grade range were missing, values were assigned in one of four ways: taking information from earlier PSS data, using information from the school’s name (e.g., middle school) to assign a grade
3 BIE schools that fit the SASS definition of a school were included in the 2007-08 SASS public school sample with certainty. For more information about the PSS, see http://nces.ed.gov/surveys/pss. 4