Twenty-three nations participated in the study. Twenty-one participated in the general assessments, while two other nations (Greece and Latvia) only participated in one or both of the advanced assessments.

To identify comparable groups across countries for the three assessments, TIMSS countries were asked to identify eligible students in terms of common definitions, after adapting the definitions to country-specific situations. Students in the mathematics and science general knowledge assessments were to be in their final year of secondary school. For the advanced mathematics assessment, eligible students were those who had taken or were taking advanced courses in mathematics. For the physics assessment, students were those who had taken or were taking physics.

The international guidelines specified the following sampling standards:

• the sample was to be representative of at least 90 percent of students in the total population eligible for the study. Therefore, exclusion rates must be under 10 percent.
• the school participation rate without the use of replacement schools must be at least 50 percent, and
• the combined participation rate (the product of school and student participation rates after replacements) must be at least 75 percent, or school and student participation rates must each be 85 percent.
• Countries were also required to submit a sampling plan for approval by the TIMSS International Study Center.

Most of the TIMSS countries experienced some deviation from international guidelines for execution of the study, at the end of secondary school, in one or more of the assessments. All deviations from these guidelines are bolded in the tables in Appendix 1.

A1.1: Nations' Definitions Of Eligible Students And Whether Met Sampling Standards: Mathematics And Science General Knowledge Assessments

A1.2: Nations' Definitions Of Eligible Students And Whether Met Sampling Standards: Advanced Mathematics Assessment

A1.3: Nations' Definitions Of Eligible Students And Whether Met Sampling Standards: Physics Assessment

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