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Student Base Weights

Every sampled student received a student base weight, whether or not the student participated in the assessment. The student base weight reflects the number of students that the sampled student represents in the population for purposes of estimation. The summation of the student base weights over a particular student group provides an estimate of the total number of students in that group in the population.

The student base weight STUWGTjsk (jurisdiction j, school s, student k) is a product of the following factors:

  • the school base weight pi subscript j s superscript -1 (the inverse of the school's probability of selection);
  • the school nonresponse adjustment factor SNRADJjs;

  • the substitution adjustment factor to account for the difference in size between the substitute and its corresponding original school SUBADJjs;

  • the school trim factor TRIMjs;

  • the within-school sampling interval WINSCHLjs for selecting students;

  • a factor for year-round schools YRRNDjs; and

  • the subject factor SUBJFACj.

To summarize:

STUWGT subscript jsk equals pi inverse subscript js times SNRADJ subscript js times SUBADJ subscript js times TRIM subscript js times WINSCHL subscript js times YRRND subscript js times SUBJFAC subscript j

The within-school sampling interval WINSCHLs is the inverse of the student sampling rate—whether national main assessment or state assessment—in the school.

For cooperating substitutes of nonresponding sampled original schools, SUBADJjs accounts for the difference in size between the participating substitute school and the nonparticipating original school. It is equal to the ratio of the estimated grade enrollment for the originally sampled school to the estimated grade enrollment for the substitute school. The student sample from the substitute school then "represents" the set of grade-eligible students from the originally sampled school.

The year-round factor YRRNDjs adjusts the student weight for students who do not attend school during the time of the assessment in year-round schools. This situation typically arises in overcrowded schools. Administrators in year-round schools randomly assign students to portions of the year in which they attend school and portions of the year in which they do not attend. At the time of assessment, a certain percentage of students (designated as OFF) does not attend school and thus cannot be assessed. The YRRNDjs factor is 1/(1-OFF) for the school. The weights including this factor allow the assessed sample to represent the full student body within the originally sampled schools.

The subject factor SUBJFACj adjusts the student weight to account for the assignment of students within the school to either mathematics or reading. The subject factor varies by subject, school type (public/private), and jurisdiction (Puerto Rico/all others).


Last updated 06 November 2008 (RF)

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National Center for Education Statistics - http://nces.ed.gov
U.S. Department of Education