VietTESOL International Convention 2025

This study tested the falsifiable and null hypotheses of Yanagisawa and Webb’s (2021) statistical model ILH Plus which aimed to predict the effectiveness of incidental vocabulary learning activities. According to this model, learning activities with a higher ILH-Plus score will produce larger vocabulary gain than those with a lower ILH-Plus score, with other factors in the activities being equal (falsifiable hypothesis) or regardless of other factors not included in the model (null hypothesis). To this end, the study employed two counter-balanced pretest-posttest experiements to gauge the vocabulary gain out of 20 non-words from a gap-filling (ILH-Plus score of 38.6 points) and a sentence-writing task (ILH-Plus score of 45.6 points), which shared the same amount of time-on-task (Experiment 1, N = 70, to test the falsifiable hypothesis), and to assess the learning outcome out of the same 20 non-words, but from a sentence-writing and a composition-writing task (ILH-Plus score of 53.6 points) and without the above time-on-task control (Experiment 2, N = 64, to test the null hypothesis). A meaning-recall test was administered after each experiment to measure lexical uptake and two weeks later for vocabulary retention. The results from both experiments showed that all learning activities yielded sizeable vocabulary gains, but in a descending order of the gain size as Composition-writing > Sentence-writing > Gap-filling, regardless of the time-on-task control. Therefore, both hypotheses were supported, suggesting that ILH Plus is indeed a reliable predictor for the effectiveness of incidental vocabulary learning activities and can be used to inform vocabulary instruction.