he guessing from context test Yosuke Sasao and Stuart Webb Kyoto University, Japan | he University of Western Ontario, Canada his study aims to develop two equivalent forms of the Guessing from Con- text Test (GCT) and provide its preliminary validity evidence. he GCT is a diagnostic test of the guessing skill and measures the following three impor- tant steps in guessing: identifying the part of speech of an unknown word, inding its discourse clue, and deriving its meaning. he test was adminis- tered to 428 Japanese learners of English. he results indicate that the two forms each with 20 question sets are equivalent in terms of item diiculty distribution and representativeness of the construct being measured. A wide range of validity evidence was provided using Messick’s validation frame- work, the Rasch model, qualitative investigations into the relationships to actual guessing, and proposals for score interpretation. Keywords: vocabulary, guessing from context, diagnostic test, equivalent forms, validation. 1. Introduction he skill of guessing the meanings of unknown words from context plays an important part in vocabulary learning through reading and listening, because it is the most frequent and preferred strategy when learners deal with unknown words in context (Cooper, 1999; Fraser, 1999; Paribakht & Wesche, 1999). How- ever, learners oten fail in guessing. For example, Nassaji (2003) reported that the success rate was only 25.6% (44.2% even if partially correct guesses were included). Parry (1991) found that the success rate ranged from 12% to 33%. hese low rates suggest a need for improvement in the guessing skill. Although successful guesses do not always lead to learning (e.g., Brown, War- ing, & Donkaewbua, 2008; Horst, Cobb, & Meara, 1998; Waring & Takaki, 2003), guessing makes a signiicant contribution to word retention. Guessing is a produc- tive strategy that requires an active cognitive process including hypothesis testing about word meaning (Ellis, 1994; Haastrup, 1991). Meeting words in context pro- vides a cognitive hook for word retention (Schouten-van Parreren, 1996). Guess- https://doi.org/10.1075/itl.00009.sas ITL - International Journal of Applied Linguistics 169:1 (2018), pp. 115–141. issn 0019-0829 | e-issn 1783-1490 © John Benjamins Publishing Company