The skills taught in Dialectical Behavior groups have been shown to reduce suicidal thoughts and self-harm behaviors. Which skills, exactly, are leading to that benefit? Is any one skill especially effective at this, or is there a more complex, synergistic effect?
In DBT, there are several components to mindfulness. Clients are first taught to observe, and then to describe. They are taught to do so non-judgmentally. To quote Marsha Linehan, to observe without judgment means "taking a non-evaluative approach, judging something as neither good nor bad... looking at consequences of behaviors and events."
One recent study examined non-suicidal self injury (NSSI) and DBT mindfulness skills. Eighty-four patients with borderline personality disorder were assigned to either a DBT skills group, or to the control group. After 20 weeks, they were given the Kentucky Inventory of Mindfulness Skills, which measures four mindfulness traits: observing, describing, acting with awareness, and accepting without judgment. The last skill, accepting without judgement, is similar to the DBT concept of non-judgment.
After treatment, there was a statistically significant reduction in self-injury behaviors. The reduction was correlated with scores on the "accepting without judgment" sub-scale, but no others. This suggests the DBT skill of observing non-judgmentally may be especially important in reducing self harm. It seems logical that being less judgement of ones thoughts and emotions would lead to less distress.
However, one could also argue observing and describing are prerequisite skills. After all, how can you work on being less judgmental of your thoughts and emotions until you are able to reliably observe and describe them?