Explanatory factors for the observed effects of meditation and their particular importance in behaviour therapy research include the following 3 categories:
Category 1. Factors which are common to all strategies such as social support or therapeutic contact. Many clinical researchers have observed that controls with high face validity seem more likely to generate effects of similar magnitude to the intervention. Expectancy alone has also been shown in a number of studies positively to influence the apparent effect of meditation. An important factor which relates to the plausibility of the control interventions is the participant’s expectation that they will experience a benefit (or detriment)45. Despite this, only 24 studies took specific steps to gauge either the participants’ expectation of benefit or the perceived credibility of the various interventions.
Category 2. The possibility that strategies that draw volunteers from the community without using a predetermined threshold of dysfunction end up recruiting samples containing significant proportions of participants with sub-clinical scores. These “worried well”46 have little scope to improve, exerting a ceiling effect on the chosen measures and thus dilute any apparent effect of the intervention. In other words, behaviour therapy trials, especially trials that recruit from the general community, and even more especially those community-recruited trials seeking to demonstrate behavioural changes in normal participants (i.e. those with no diagnosed psychopathology) are fundamentally prone to type 2 errors in study design47. Since meditation was developed as a practice for everyday use by normal people rather than those with psychopathology, researchers have frequently recruited from the community. This issue is therefore of particular relevance to the work presented in this thesis.
Category 3. Other factors include regression to the mean. This is a phenomenon that most commonly occurs in studies in which participants are selected because they have extreme values on a certain variable, such as in clinical trials for which specific eligibility criteria are set. In this case, the participants will manifest an improvement simply because of the natural tendency for variables to approach the population mean over time, regardless of any effect (or lack thereof) from the intervention being studied48,and poor choice of outcome measures which are not specific and sensitive enough to detect change.