Proxy variables in measuring L2 proficiency: The price of convenience

Language proficiency in L2 research is often measured indirectly through self-ratings, academic achievement, or perceived competence. While convenient, these proxies may distort learners’ actual ability and theoretical conclusions. This study examined how accurately 228 English learners estimated their proficiency and how substituting proxies for an objective measure affected findings. Language learning emotions were used to exemplify the effects of this substitution in explanatory models. Participants completed the Oxford Placement Test and self-reports of CEFR level, communication competence, and academic achievement. Only 37 % estimated their proficiency correctly, with lower-level learners overestimating and advanced learners underestimating. Correlations between the Oxford Placement Test and proxy variables were modest and structural equation models using proxies in place of objective proficiency produced results differing in strength and directionality. The findings highlight the price of convenience: while proxies are practical, they can alter study outcomes and compromise validity, underscoring the need for greater methodological caution.