7.4 limitations
    the results of the current study should be interpreted in light of the following three major limitations.
    (a) the metacognitive listening strategy training was limited to a relatively short period of time (five minutes), and furthermore, it occurred independently of the students' curriculum. it might be that the effect of metacognitive strategy training will only emerge weeks or months later when the learners are able to employ strategies on their own. therefore, it is suggested that, in future, studies design longer training to detect effects in learners' actual use of the strategies and the application of strategy training should be incorporated into course instruction.
    (b) it is very difficult for students to report doing something that they have not been consciously monitoring. regarding the data gathered on the participants' metacognitive listening awareness, the study only employed a questionnaire with no observation of the learners' actual listening performance. the questionnaire may only reflect what the participants thought they should do instead of what they actually do. however, as lynch and mendelsohn (2002, p.202) remarked, “the fact that listening comprehension occurs largely unobserved means that it can be very difficult to establish the‘process’by which listeners reach their interpretations, even if we have the evidence of the‘product’”.
    (c) another limitation of this study concerns the reliability of the vocabulary delayed posttests. becausethe participants were engaged in recycling recently met vocabulary, they may have studied some of the target words outside of the context of the experiment in the one-week interval between the immediate and delayed posttests. although this probably did not occur to any great degree, it is nevertheless, a possibility that must be acknowledged.