It should be noted that two of the four studies investigating depression focused on patients with chronic or treatment-resistant depression (Barnhofer et al., 2009; Kenny & Williams, 2007), and therefore the effect sizes for these studies might be lower than would otherwise be expected. It should also be noted that the effects of MBT on depression and anxiety in chronic conditions, such as cancer, might be smaller because patients may experience physical symptoms listed on depression or anxiety scales as a result of their physical condition or as potential side-effects of medical treatments. In addition, effect sizes for depression and anxiety symptoms in populations with cancer, pain, or other medical conditions may be smaller than effect sizes in populations with anxiety or mood disorders due to a floor effect: that is, patients with a low level of anxiety or depression at pre-treatment may show a relatively smaller degree of improvement after treatment than those with a high level at pre-treatment.
