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Methods in Brief

TIMSS and TIMSS Advanced are sample-based assessments, meaning that only a sample of students take the assessments but that they are selected in such a way as to allow the results to be generalizable to a larger target population. The TIMSS and TIMSS Advanced target populations are based on standardized definitions, and the sampling is conducted based on standardized and refereed procedures.

TIMSS required participating countries and other education systems to draw probability samples of students who were nearing the end of their fourth or eighth year of formal schooling, counting from the first year of the International Standard Classification of Education (ISCED) Level 1.3 In the United States, one sample was drawn to represent the nation at grade 4 and another at grade 8.4 In addition to these two national samples, separate state public school samples were drawn for Florida at both grades in order to benchmark that state's student performance internationally.

TIMSS Advanced required participating countries and other education systems to draw samples of students in their final year of secondary school—International Standard Classification of Education (ISCED) Level 3—who have taken courses in advanced mathematics or who have taken courses in physics. In the United States, two samples were drawn to represent the nation—one for advanced mathematics and one for physics.5 The courses that define the target populations have to cover most, if not all, of the advanced mathematics and physics topics that were outlined in the TIMSS Advanced 2015 Assessment Frameworks. In the United States, this was defined as a calculus course for eligibility for advanced mathematics and an advanced physics course similar to AP physics for physics.

For additional details on the methods used in TIMSS and TIMSS Advanced 2015, see the Methodology and Technical Notes.


3 The ISCED was developed by the United Nations Educational, Scientific, and Cultural Organization (UNESCO) to assist countries in providing comparable, cross-national data. ISCED Level 1 is termed primary schooling, and in the United States is equivalent to the first through sixth grades. In most education systems, including the United States, these students were in the 4th and 8th grades. Details on the average age at the time of testing in each education system are included in the Methodology and Technical Notes.
4 At grade 4, a total of 250 schools and 10,029 students participated in the United States in 2015. At grade 8, a total of 246 schools and 10,221 students participated. The overall weighted school response rate in the United States at grade 4 was 77 percent before the use of substitute schools and 85 percent after the use of substitute schools. The weighted student response rate at grade 4 was 96 percent. The overall weighted school response rate at grade 8 before the use of substitute schools was 78 percent and 84 percent after the use of substitute schools. The weighted student response rate at grade 8 was 94 percent.
5 A total of 241 schools participated in the advanced mathematics assessment in TIMSS Advanced 2015; and 165 schools participated in the physics assessment. Within those schools, 2,954 students participated in the advanced mathematics assessment and 2,932 students participated in the physics assessment. For advanced mathematics, the overall weighted school response rate in the United States was 72 percent before the use of substitute schools and 76 percent after the use of substitute schools. For physics, the overall weighted school response rate was 65 percent before the use of substitute schools and 68 percent after the use of substitute schools. The weighted student response rate was 87 percent for the advanced mathematics assessment and 85 percent for the physics assessment.