<p>The main purpose of this paper was to construct and try out a test that could measure the size of both the receptive and productive vocabulary. This was a joint project, done by three students at the C-level in English in 1997. Before the test was constructed the students looked into previous investigations and different test methods used. The project group chose the Yes/No method as their test format. 23 students in their second year of their education at a theorectical programme in upper secondary school and 16 adult students at Komvux took the test in this paper. The results of the test taken by the students showed that it is impossible for a language teacher to construct a reliable and valid test for measuring vocabulary size using the Yes/No method.</p>

The main purpose of this paper was to construct and try out a test that could measure the size of both the receptive and productive vocabulary. This was a joint project, done by three students at the C-level in English in 1997. Before the test was constructed the students looked into previous investigations and different test methods used. The project group chose the Yes/No method as their test format. 23 students in their second year of their education at a theorectical programme in upper secondary school and 16 adult students at Komvux took the test in this paper. The results of the test taken by the students showed that it is impossible for a language teacher to construct a reliable and valid test for measuring vocabulary size using the Yes/No method.