Despite the introduction of mirror therapy in the late 1990s, little research was published on it before 2009, and much of the research since then has been of contested quality. Out of 115 publications between 2012 and 2017 about using mirror therapy to treat phantom limb pain, a 2018 review, found only 15 studies whose scientific results should be considered. From these 15 studies, the reviewers concluded that "MT seems to be effective in relieving PLP, reducing the intensity and duration of daily pain episodes. It is a valid, simple, and inexpensive treatment for PLP." Similarly, a 2017 review that studied a wider range of uses for mirror therapy, concluded, "Mirror therapy has been used to treat phantom limb pain, complex regional pain syndrome, neuropathy and low back pain. The mechanism of action of mirror therapy remains uncertain, and the evidence for clinical efficacy of mirror therapy is encouraging, but not yet definitive."