Many of the early studies lack a theoretically unified perspective, often resulting in poor methodological quality, as discussed above in the section Definition and scope.

It showed promise in early studies, though later trials of higher methodological quality have had mixed results.

Studies of high methodological quality were more likely to be negative than the lower quality studies.

The methodological quality of the primary research was generally low, with such problems as weaknesses in study design and reporting, small sample size, and selection bias.

The report concluded, "Scientific research on meditation practices does not appear to have a common theoretical perspective and is characterized by poor methodological quality.

They were single centre trials with poor methodological quality.

This problem is likely to be encountered often by decision makers wishing to assess the methodological quality of published studies.

Later trials of higher methodological quality indicated no difference from placebo.

No adverse events were reported, and most trials were positive but of low methodological quality.

Many controlled clinical studies of spinal manipulation have been conducted, but their results often disagree and they are typically of low methodological quality.