Chiropractic is a complementary health approach or form of medicinal treatment mostly concerned with the diagnosis and repair of mechanical disorders of the musculoskeletal system, especially in the spine. Spinal manipulation, which chiropractors call “spinal adjustment” or “chiropractic adjustment”, is the most common treatment used in chiropractic care, and back and neck pain, in particular, has been proven to be effectively treated by chiropractic manipulation. These manipulations are specifically applied to the spine or other parts of the body with the goal of correcting alignment problems, alleviating pain, improving function, and supporting the body’s natural ability to heal itself. It requires an in-depth education in anatomy and physiology and tends to overlap with other manual-therapy professions such as massage therapy, osteopathy, and physical therapy. According to the 2007 National Health Interview Survey (NHIS), which included a comprehensive survey of the use of complementary health approaches by Americans, about 8 percent of adults (more than 18 million) and nearly 3 percent of children (more than 2 million) had received chiropractic or osteopathic manipulation in the past 12 months. Additionally, an analysis of NHIS cost data found that adults in the United States spent approximately $11.9 billion out-of-pocket on visits to complementary health practitioners—$3.9 billion of which was spent on visits to practitioners for chiropractic or osteopathic manipulation. Chiropractors may combine the use of spinal adjustments and other manual therapies with several other treatments and approaches such as heat and ice, electrical stimulation, muscular relaxation techniques, rehabilitative and general exercise, fitness counseling about diet, weight loss, and other lifestyle factors, and dietary supplements. Though considered by some to be an alternative medicine, the World Health Organization found chiropractic care to be safe when employed skillfully and appropriately.