Creation and validation of a bilingual test to estimate aural and written vocabulary size

Language learners’ vocabulary size is a reliable predictor of their success in second language as it clearly correlates with better performances the target language. Being precise those estimations paramount to plan teaching. However, instruments employed by previous studies for might present validity and reliability issues that affect research sensitivity accuracy.
 This paper presents step-by-step account creation an aural written version bilingual test. Test was delivered 73 adult L1-Spanish students attending English classes. Their answers were analysed Rasch model determine best performing items test so overall instrument enhanced.
 The final high levels reliability: .89 listening .82 Furthermore, descriptive statistics confirm recognizing words form more challenging than form: participants got 10.80% fewer correct finding confirms claim are two separate dimensions, impacts on how should be taught L2 classrooms.