Last year saw the publication of the first large meta-analysis of DDL (Boulton & Cobb, 2017) and it had generally positive findings for the field; for example (emphasis added):
Focusing only on the most robust results (i.e., MVs with at least 10 unique samples in both P/P and C/E designs), 70% had large effects, 25% medium, and only 5% small or negligible. The most consistent large effects showed that DDL is perhaps most appropriate in foreign language contexts for undergraduates as much as graduates, for intermediate levels as much as advanced, for general as much as specific/academic purposes, for local as much as large corpora, for hands-on concordancing as much as for paper-based exploration, for learning as much as reference, and particularly for vocabulary and lexicogrammar. Many of these findings go against common perceptions, and the elements missing from the list (e.g., skills or other language areas) are for the most part missing because there is as yet insufficient research rather than because research evidence is against them.
I bolded “vocabulary and lexicogrammar” because in the past week another meta-analysis was published. This meta-analysis looked at corpus use and vocabulary learning (Lee, Warschauer, & Lee, 2018). They found that:
[O]ur meta-analysis showed a medium-sized effect on L2 vocabulary learning, with the greatest benefits for promoting in-depth knowledge to learners who have at least intermediate L2 proficiency. Corpus use was also more effective when the concordance lines were purposely selected and provided and when learning materials were given along with hands-on corpus-use opportunities. Moreover, we found that corpus use is still effective even without prior training and remains effective regardless of the corpus type or the length of the intervention.
The details of both papers are worth digging into, especially if one is statistically-minded. Furthermore, Boulton & Cobb make a number of recommendations for what kinds of studies and data could benefit the field in the future, while Lee, Warschauer, & Lee also mention that certain types of data/studies could help with the problem of small-sample sizes in future meta-analyses. In other words, if you do or are interested in doing DDL or corpus-use research, these papers point out gaps where research could be done and would be useful.
So the gist is that both papers are excellent contributions to understanding the effects of DDL and moderating influences, and they point to future research needs.
(Links are above)
Boulton, A., & Cobb, T. (2017). Corpus Use in Language Learning: A Meta‐Analysis. Language Learning, 67(2), 348-393.
Lee, H., Warschauer, M., & Lee, J.H. (2018). The Effects of Corpus Use on Second Language Vocabulary Learning: A Multilevel Meta-analysis. Applied Linguistics.