Answers are grounded in this paper and cite their sources.
Article ON MEASURING VOCABULARY DIFFICULTY. AN ANALYSIS OF ITEM VARIABLES IN LEARNING RUSSIAN-ENGLISH VOCABULARY PAIRS was published on January 1, 1969 in the journal International Review of Applied Linguistics in Language Teaching (volume 7, issue 4).
No takes yet. Share an insight, caveat, or question.
Theodore S. Rodgers (1969) studied this question.
Synapse has enriched 10 related papers. Consider them for comparative context: