雖然都是測量詞語的知識，但是不同測驗間還是會些許的差別，Paul,Stallman and Rourke (1990) 比較二語學習者的選擇題、面試以及自評是否知道這個詞(Yes/No)三種測驗，發現三者的相關係數介於.66到.81之間。但是Nist and Olejnik (1995) 的研究，對於母語者在同樣的詞彙下進行造句、完成句子、意義與範例的四種測驗，則發現彼此的相關通通低於.7。Laufer and Goldstein (2004) 也在他們研究中的四種測驗發現測驗間的相關不高。
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