Conclusion: Most clinical trials on meditation practices are generally characterized by poor methodological quality with significant threats to validity in every major quality domain assessed. Despite a statistically significant improvement in the methodological quality over time, it is imperative that future trials on meditation be rigorous in design, execution, analysis, and the reporting of results.
I went to the first reference from your wikipedia link
https://www.ncbi.nlm.nih.gov/pubmed/19123875
Conclusion: Most clinical trials on meditation practices are generally characterized by poor methodological quality with significant threats to validity in every major quality domain assessed. Despite a statistically significant improvement in the methodological quality over time, it is imperative that future trials on meditation be rigorous in design, execution, analysis, and the reporting of results.
Second reference from wikipedia
http://ebooks.cambridge.org/chapter.jsf?bid=CBO9780511816789...
The Cambridge Handbook of Consciousness,
Cambridge Handbooks in Psychology