Biases in estimating self and others’ second language vocabulary knowledge.

Estimating what others know is essential for effective communication, yet people often misjudge their audience's knowledge, increasing the risk of miscommunication. This challenge is heightened in bilingual contexts, where vocabulary knowledge can vary widely, and inaccurate estimations may lead to communication breakdowns. Despite its importance, little is known about how bilinguals estimate others' vocabulary knowledge. Study 1 investigated how bilinguals estimated their own and others' second language vocabulary when the language background of the others was similar (Experiment 1.1), unknown (Experiment 1.2), or different (Experiment 1.3) from their own. Study 2 examined whether providing objective information influenced these estimations. Results revealed consistent biases, shaped by similarity in language background. Confidence in self-knowledge emerged as a key factor in estimating others' knowledge, and objective information did not affect the estimation. By integrating metacognition and knowledge estimation theories, the study sheds light on vocabulary estimation and offers insights into knowledge estimation processes. (PsycInfo Database Record (c) 2026 APA, all rights reserved).