Chronic pain is pain that lasts a suspire time. In medicine the distinction between acute and chronic pain is sometimes persistent by an arbitrary interval of time since onset; the two most commonly used markers being 3 months and 6 months since onset though some theorists and researchers have placed the transition from acute to chronic pain at 12 months. Others apply acute to pain that lasts less than 30 days, chronic to pain of more than six months duration and subacute to pain that lasts from one to six months. A popular alternative definition of chronic pain, involving no arbitrarily fixed duration is "pain that extends beyond the expected period of healing". Epidemiological studies have found that 8% - 11.2% of people in various countries have chronic widespread pain.