The ICILS 2018 U.S. public-use student, teacher, and school data files include U.S. specific variables that are not part of the U.S. data files in the ICILS 2018 international database. They are add-on files that do not contain weight variables or replicate weights, and therefore must be merged with the U.S. data files in the international database before any analysis can be conducted. The U.S. data files in the international database can be downloaded from the IEA Data Repository
https://www.iea.nl/data-tools/repository.
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