Reliability of Data
SASS estimates are based on samples. The sample estimates may differ somewhat from the values that would be obtained from the universe of respondents using the same questionnaire, instructions, and field representatives. The difference occurs because a sample survey estimate is subject to two types of errors: nonsampling and sampling. Estimates of the magnitude of sampling error for SASS data can be derived or calculated. Nonsampling errors are attributed to many sources, including definitional difficulties, the inability or unwillingness of respondents to provide correct information, differences in the interpretation of questions, an inability to recall information, errors made in collection (e.g., in recording or coding the data), errors made in processing the data, and errors made in estimating values for missing data. Quality control and edit procedures were used to reduce errors made by respondents, coders, and interviewers.
Caution Concerning Changes in Estimates
Care must be taken in estimating change over time in a SASS data element, because some of the measured change may not be attributable to a change in the education system. Some of the change may be due to changes in the sampling frame, changes in questionnaire item wording, or other changes. For example, the definition of locale codes has undergone major changes since the 2000 Decennial Census. The first major change was an improvement in geocoding technology, which improved the assignment of specific addresses to physical locations. In 2005, a new locale code for CCD was implemented based on the new urban-centric method of classifying locale. Changes in how areas and, thus, schools are categorized may account for at least some changes that are noted from previous administrations.
To facilitate the transition from the older locale codes to the new ones, locale codes based on geographic concepts from both the 2000 Decennial Census and the new urban-centric method are included in the 2007-08 SASS data files. (SLOCP8, URBANS8, DLOCP8, and URBAND8 use the 2000 Census metropolitan areas, and SLOCP12, URBANS12, DLOCP12, and URBAND12 use the new urban-centric method.) The specific categories reported by the 2000 Census locale codes are based upon the 2000 Census definitions for central city, urban fringe of a large or medium-sized central city, large or small town, and rural areas either inside a metropolitan area or outside a metropolitan area. The new urban-centric locale codes are based on the more immediate proximity of a physical location to an urbanized area than are the older, county-based locale codes. This report uses the new urban-centric locale codes.