It is difficult to make conclusions about meditation when the definition of the independent variable itself varies from study to study, if not from person to person. A homogeneous definition of meditation is essential for further progress in this field and yet, after almost 40 years of research the scientific community is unable to provide a truly consensus definition. Some argue that this is because meditation is actually a broad collection of disparate methods however it might be equally argued that the lack of consistent definition is symptomatic of our poor understanding.
More discussion on the definition of meditation can be found at Dr Ramesh Manocha’s blog.