Objective: The reliable change index (RCI) is a simple statistical computation which estimate if changes in two psychometric measures are probably due to measurement error or can be accounted by other factor, as a clinical intervention. Despite its clinical usefulness, the method is underutilized by psychiatrists and psychologists. We consider the use of the RCI in clinical practice by a case report of cognitive-behavioral therapy. Method: a female patient of 40 years old sought

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... oral therapy due to symptoms of depression. We structured the intervention in 16 sessions and used Beck Depression Inventory II (BDI-II) for the assessment of depressive symptoms and answered in each session. Using published data about the BDI-II reliability and its standard deviation, we calculated the RCI before and after the intervention. Results and conclusions: The patient started the treatment with moderate to severe symptoms of depression and showed almost a linear decrease of the symptoms along the sections. Although no reliable change could be associated with the first month of treatment, starting at the second month, we documented a reliable decrease in the depressive symptoms from session 4 to 16. The RCI index it's a useful method to assess if changes in psychometric measures may represent real change or occur by measurement error.