Probably the most thorough and up to date review of meditation research was published in 2007 by a team led by Maria Ospina, specifically contracted by the US Department of Health and Human Services to assess the evidence base. They included both randomized and non-randomized trials. In their assessment of more than 800 studies they concluded:
Many uncertainties surround the practice of meditation. Scientific research on meditation practices does not appear to have a common theoretical perspective and is characterized by poor methodological quality. Firm conclusions on the effects of meditation in healthcare cannot be drawn based on the available evidence.