Hypothesis 2 predicted that the meditators' postintervention scores on self-report measures of metacognitive processing would be significantly more improved postintervention than those of the nonmeditators. Again, the results only partially supported this expectation. As predicted, the meditators demonstrated a significant postintervention increase in mindfulness relative to the nonmeditators, with a medium-to-large effect size for the time by group interaction. This can be taken to suggest that the intervention resulted in enhanced mindfulness, consistent with previous literature (Baer, 2003; Grossman, 2004).
Interestingly, however, the meditators did not demonstrate a significant decrease in rumination, compared to the nonmeditators, following the intervention. The extremely small effect size for the time by group interaction suggests that the nonsignificance of the time by group interaction was not due to insufficient sample size. This conflicts with previous literature, which has suggested that mindfulness and rumination are mutually exclusive modes of processing (Roemer & Orsillo, 2002). Again, this suggests the possibility that the intensive nature of the Vipassana meditation course somehow generates different effects, at least in the period immediately following the course, than the mindfulness-based interventions described in the literature. This highlights the need for further studies, particularly those which employ longitudinal designs.