abstract
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When measuring academic skills among students whose primary language is not English, standardized assessments are often provided in languages other than English (Tabaku, Carbuccia-Abbott, & Saavedra, 2018). The degree to which alternate-language test items function equivalently must be evaluated, but traditional methods of investigating measurement equivalence may be confounded by group differences on characteristics other than ability level and language form. The primary purposes of this study were to investigate differential item functioning (DIF) and item bias across Spanish and English forms of an assessment of early mathematics skills. Secondary purposes were to investigate the presence of selection bias and demonstrate a novel approach for investigating DIF that uses a regression discontinuity design framework to control for selection bias. Data were drawn from 1,750 Spanish-speaking Kindergarteners participating in the Early Childhood Longitudinal Study, Kindergarten Class of 1998-99, who were administered either the Spanish or English version of the mathematics assessment based on their performance on an English language screening measure. Results indicated a minority of items functioned differently across the Spanish and English forms, and subsequent item content scrutiny indicated no plausible evidence of item bias. Evidence of selection biasdifferences between groups in SES, age, and country of birth, in addition to mathematics ability and form languagehighlighted limitations of a traditional approach for investigating DIF that only controlled for ability. Fewer items exhibited DIF when controlling for selection bias (11% vs. 25%), and the type and direction of DIF differed upon controlling for selection bias.