We read the article by Ninomiya et al. with great interest and appreciate the author's efforts to analyze the effect of primary mindfulness-based cognitive therapy (MBCT) in patients with anxiety disorder in secondary-care settings, compared with a waiting-list group. However, we have concerns about baseline imbalance of depressive symptoms that may influence the conclusion of the trial.
Comorbid major depressive disorder can have caused an underestimation of anxiety symptoms in the waiting-list group and distort effectiveness of MBCT. The wait-list group had more severe depressive symptoms than the intervention group, about 7 points more in the Center for Epidemiologic Studies Depression Scale (CES-D) scores, and that group might have more major depressive disorder. Indeed, the rate of antidepressant use in the wait-list group was 25% higher than the intervention group.
It is well known that major depressive disorder is associated with cognitive errors and underestimation of self-report outcomes. Baseline imbalance of depressive symptoms may therefore weaken the conclusion of the study, because all outcome measures were self-report questionnaires.
The authors should acknowledge the limitation and provide information about the diagnosis of major depressive disorder.