phase of desensitization. Phases 5 and 6 involve installing positive cognitions and 'body scan". The last phase is the reevaluation phase. EMDR is typically undertaken in a series of sessions with a trained therapist. The number of sessions can vary depending on the progress made. A typical EMDR therapy session lasts from 60 to 90 minutes. Medical uses Trauma and PTSD The person being treated is asked to recall an image, phrase, and emotions that represent a level of distress related to a trigger while generating one of several types of bilateral sensory input, such as side-to-side eye movements or hand tapping. The 2013 World Health Organization practice guideline says that "Like cognitive behavioral therapy (CBT) with a trauma focus, EMDR aims to reduce subjective distress and strengthen adaptive beliefs related to the traumatic event. Unlike CBT with a trauma focus, EMDR does not involve (a) detailed descriptions of the event, (b) direct challenging of beliefs, (c) extended exposure or (d) homework." Effectiveness While multiple meta-analyses have found EMDR to be as effective as trauma focused cognitive behavioral therapy (TF-CBT) for the treatment of PTSD, these findings have been regarded as tentative given the low numbers in the studies, high-risk rates of researcher bias, and high dropout rates. A Cochrane systematic review comparing EMDR with other psychotherapies in the treatment of Chronic PTSD found EMDR to be just as effective as TF-CBT and more effective than the other non-TF-CBT psychotherapies. Caution was urged interpreting the results due to low numbers in included studies, risk of researcher bias, high drop-out rates, and overall "very low" quality of evidence for the comparisons with other psychotherapies. A 2016 systematic review and meta-analysis found that the effect size of EMDR for PTSD is comparable to other evidence-based treatments, but that the strength of evidence was of a low quality, indicating that the effect sizes achieved are associated with substantial uncertainty. A 2020 systematic review and meta-analysis was the "first systematic review of randomized trials examining the effects of EMDR for any mental health problem." The authors raised concerns about bias in previous studies, concluding: Some smaller studies have produced positive results. Position statements The 2009 International Society for Traumatic Stress Studies practice guidelines categorized EMDR as an evidence-based level A treatment for PTSD in adults. Other guidelines recommending EMDR therapy – as well as CBT and exposure therapy – for treating trauma have included