The available evidence also indicates that children show different levels of adjustment to chronic pain over time. Chronic idiopathic musculoskeletal pain has been shown to persist in 59% of cases for as long as nine years; in this study, the authors found the children to have pain and disability levels comparable to children with juvenile chronic arthritis, but lower levels of psychosocial functioning. Hunfeld, Perquin, and colleagues in Rotterdam have traced the persistence of chronic benign pain in 30-45% of cases for up to two years and three years, with no increase in intensity or frequency. In the latter study, open-ended interviews elicited information about functioning and coping skills, and identified continuing problems with physical activity, mental concentration, social interaction, and psychological stress (becoming "moody"), particularly when the pain was severe. The researchers found, however, that several children had developed their own strategies to maximize functionality despite the continuing pain: "…pain had become part of the daily lives of several adolescents, who structured their activities and sleeping hours to prevent aggravation of pain". A recent cluster analysis of 117 children with chronic pain divided them into three groups on the basis of a set of psychosocial and behavioral measures: those who were highly distressed and disabled; those who showed low levels of distress and disability; and those who showed only moderate levels of distress and disability, but whose family environment scored low on cohesion.