Measuring bilingual language dominance: An examination of the reliability of the Bilingual Language Profile

Measuring language dominance, broadly defined as the relative strength of each of a bilingual's two languages, remains a crucial methodological issue in bilingualism research. While various methods have been proposed, the Bilingual Language Profile (BLP) has been one of the most widely used tools for measuring language dominance. While previous studies have begun to establish its validity, the BLP has yet to be systematically evaluated with respect to reliability. Addressing this methodological gap, the current study examines the reliability of the BLP, employing a test-retest methodology with a large (N = 248), varied sample of Spanish-English bilinguals. Analysis focuses on the test-retest reliability of the overall dominance score, the dominant and non-dominant global language scores, and the subcomponent scores. The results demonstrate that the language dominance score produced by the BLP shows "excellent" levels of test-retest reliability. In addition, while some differences were found between the reliability of global language scores for the dominant and non-dominant languages, and for the different subcomponent scores, all components of the BLP display strong reliability. Taken as a whole, this study provides evidence for the reliability of BLP as a measure of bilingual language dominance.