Every sampled student received a student base weight, whether or not the student participated in the assessment. The student base weight is the reciprocal of the probability that the student was sampled to participate in the assessment for a specified subject. The student base weight for student k from school s in jurisdiction j (STU_BWTjsk) is the product of seven weighting components and can be expressed as follows:
The within-school student weight (WINSCHWTjs) is actually the inverse of the student sampling rate in the school.
The subject spiral adjustment factor (SUBJFACj) adjusts the student weight to account for the spiral pattern used in distributing mathematics, reading, or science booklets to the students. The subject factor varies by subject, school type (public/private), and jurisdiction (Puerto Rico/all others), and it is equal to the inverse of the proportion of math (or reading or science) booklets in the overall spiral for a specific sample.
For cooperating substitutes of nonresponding sampled original schools, the substitution adjustment factor (SUBADJjs) 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 adjustment factor (YRRND_AFjs) 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 OFFjs) do not attend school and thus cannot be assessed. The YRRND_AFjs for a school is calculated as 1/(1-OFFjs/100) for the school. The weights including this factor allow the assessed sample to represent the full student body within the originally sampled schools.