Comparability of Bilingual Versions of Assessments: Sources of Incomparability of English and French Versions of Canada's National Achievement Tests

This research examined the degree of comparability and sources of incomparability of English and French versions of reading, mathematics, and science tests that were administered as part of a survey of achievement in Canada. The results point to substantial psychometric differences between the 2 language versions. Approximately 18% to 36% of the items were identified as differentially functioning for the 2 language groups. Large proportions of these differential item functioning (DIF) items, 36% to 100% across age groups and content areas, were attributed to adaptation related differences. A smaller proportion, 27% to 33% of the DIF items, was attributed to curricular differences. Twenty-four to 49% of DIF items could not be attributed to either of the 2 sources considered in the study.