The many reviews thorough and reliable reviews of of meditation enable us to make some basic generalisations:

First, there is insufficient evidence to support the idea that meditation, as conceived and tested by scientific researchers in the West, is any more effective than simple relaxation or rest.

Second, the use of high face-validity control groups is critical in meditation research because of the need to exclude the important confounding effects of non-specific factors that relate to plausibility of the intervention (such as placebo, expectancy, or therapeutic contact).

Third, there is at the moment no systematic comparison of different conceptualizations of meditation. Only a few researchers have compared two kinds of meditation and found that there were no major differences between the two.

These observations could lead to three possible conclusions:
1. Meditation is in fact no more effective than other approaches to rest and relaxation. Yet that meditative traditions have existed for thousands of years and at least in India, are widely perceived to have specific and unique features. In other words history and culture do not agree with the idea that meditation is simply a method of mundane relaxation. While this “test of history” does not provide proof of efficacy, it does encourage the undertaking of a thorough examination of the phenomenon before it is discarded as mere folklore and superstition.
2. The measures which have so far been used to assess the effects of meditation are not sensitive to the specific effects of meditation. The wide variety of outcome measures used means that if the specific effects of meditation are not detectable, then the effects are either too small or too esoteric for mundane study. Yet classical descriptions of meditation suggest that despite the metaphysical basis of meditation, its effects do manifest themselves in mundane dimensions such as health and behaviour, implying that at least some of the many measures available to researchers should be able to detect a differential effect. Again, while this might be satisfactorily applied to the genre as a whole, there appear to be isolated exceptions which suggests that certain as yet undetermined categories may be able to generate specific effects. Yet our analysis of the aggregated data has not yet yielded a pattern with sufficient clarity to identify the features of that category.
3. The methods that have been labelled as “meditation” in the trials do not consistently reflect the true nature of meditation. This is the most interesting and important issue and therefore merits considerable discussion. The functional and conceptual definition determines the nature of the intervention, which in turn influences the choice of the control method that ought to be used and therefore the validity and generality of the findings. Yet defining meditation has proven to be a difficult challenge for modern researchers. While early empirical reports seemed to show that measurable distinctions between meditation and rest or simple relaxation existed, rigorous trials did not support these perceptions. As a result, much of the research work on meditation has been based on the assumption that meditation techniques are much the same despite minor external and superficial differences.  These perceptions have thus given rise to an assumption of “psycho-physiological uniformity”

This last idea, it is contended, is the key to the problem because in fact, both Western meditation enthusiasts and Western scientists, despite their opposing views, have failed to apprehend a key factor that underlies the ancient tradition of meditation: The idea that meditation necessarily involves the experience of mental silence.

Dr Ramesh Manocha