Depression can be described as a chronic rather than an acute illness and single, isolated episodes of depression are rare. In fact, the risk of repeated episodes is said to exceed 80% and patients can expect an average of four episodes of depression in their lifetimes. The risk of relapse has been linked to the number of prior episodes a patient has experienced and patients who have experienced three or more prior episodes have a greatly increased risk of relapse. One study reported that with each additional episode there is an 18% increase in the risk of recurrence. However, there has been little research into people's psychotherapy 'careers' and little data regarding the relationship of these prior treatments and responsiveness to psychotherapy. An Australian study of 48 individuals with major depression turning up for treatment at a community-based psychotherapy facility found that 90% of them had received some form of prior psychotherapy or counselling, with on average 3.5 previous episodes of care. Those receiving psychotherapy at the time of intake showed higher levels of improvement over the following year suggesting that those actively engaged in some therapy experience at intake benefited more than those with an 'interrupted' psychotherapy career.
Grenyer, Brin F.S., Deane, Frank P. and Lewis, Kate L. - Treatment history and its relationship to outcome in psychotherapy for depression Counselling and Psychotherapy Research March 2008, 8(1), 21-27