Strangely enough he did a very empirical study of word association tests. The notion is that through life we learn what goes together. When there is an unusual response, there is some reason for the intrusion. Test taker gives first word they think of in response to stimulus word. There are various lists of stimulus words.
Interpretation is based on unusualness of association, response latencies, nonverbal concomitants.
Despite long history, the test is not as popular as it was 20 years ago. There are various lists of stems. Most famous is the Rotter Incomplete Sentence Blank, with 40 stems. The tests are still very popular. Sentence completion methods are probably more face valid than most, which heightens their susceptibility to dissimulation.