In this meta-analysis, we give a comprehensive overview of the effects of meditation on psychological
variables that can be extracted from empirical studies, concentrating on the effects of meditation on
nonclinical groups of adult meditators. Mostly because of methodological problems, almost 3⁄4 of an
initially identified 595 studies had to be excluded. Most studies appear to have been conducted without
sufficient theoretical background. To put the results into perspective, we briefly summarize the major
theoretical approaches from both East and West. The 163 studies that allowed the calculation of effect
sizes exhibited medium average effects (r .28 for all studies and r .27 for the n 125 studies from
reviewed journals), which cannot be explained by mere relaxation or cognitive restructuring effects. In
general, results were strongest (medium to large) for changes in emotionality and relationship issues, less
strong (about medium) for measures of attention, and weakest (small to medium) for more cognitive
measures. However, specific findings varied across different approaches to meditation (transcendental
meditation, mindfulness meditation, and other meditation techniques). Surprisingly, meditation experience
only partially covaried with long-term impact on the variables examined. In general, the dependent
variables used cover only some of the content areas about which predictions can be made from already
existing theories about meditation; still, such predictions lack precision at present. We conclude that to
arrive at a comprehensive understanding of why and how meditation works, emphasis should be placed
on the development of more precise theories and measurement devices.