Defining response and remission in psychotherapy research: A comparison of the RCI and the method of percent improvement

There is no consensus as to how to define response and remission for mental disorder treatments. The Reliable Change Index (RCI) is most commonly used in psychotherapy research, whereas psychopharmacologists prefer to calculate percentage of improvement (PI). We compared both methods using the Beck Depression Inventory in 395 depressive outpatients. The overall pre-post effect size was d=1.18. The PI-50 (≥ 50% improvement from baseline) resulted in outcome estimates higher than the RCI: 66.3% vs. 59.2% for response and 50.6% vs. 45.8% for remission. We demonstrate that the PI approach is independent of arbitrarily chosen reliabilities and reference populations. Furthermore, it takes differences of pre-treatment severity into account. It is considered as a valuable extension of the established RCI in psychotherapy research.