And adjusted for differences in age, education and language proficiency, the gaps narrow.

Her study said, however, that it was 'becoming increasingly clear through research that not all pilots and controllers are able to adhere to these language proficiency standards'.

Language exchanges are generally considered helpful for developing language proficiency, especially in speaking fluency and listening comprehension.

Each level translates to an equivalent range of scores on other language proficiency exams.

As perceived language proficiency in a second languages increases, the use of that second language for inner speech becomes more habitual.