Acupuncture is one of the main branches of Traditional Chinese Medicine. The technique involves the insertion of needles into "acupuncture points" on the body by trained practitioners. According to acupunctural teachings this will restore health and well-being, and is particularly good at treating pain. The definition and characterization of these points is standardized by the World Health Organization. Acupuncture is thought to have originated in China and is most commonly associated with Traditional Chinese medicine. Other types of acupuncture (Japanese, Korean, and classical Chinese acupuncture) are practiced and taught throughout the world. Scientists have conducted reviews of existing clinical trials according to the protocols of evidence-based medicine; some have found efficacy for headache, low back pain and nausea, but for most conditions have concluded that there is insufficient evidence to determine whether or not acupuncture is effective.