In order to quantify the burden of illness in hemophilia, and to study the response to different treatments, it is necessary to have quantitative outcome measures of high validity and reliability. The International Prophylaxis Study Group (IPSG - chair Dr. Victor Blanchette) was established in 2001 with the stated purpose of developing and testing outcome tools for this purpose. The group has developed a magnetic resonance imaging (MRI) score for quantifying arthropathy (representing the domain of structure and function domain in the ICF framework), a quantitative physical examination score, and the Hemophilia Joint Health Score or HJHS, to replace the older and less sensitive World Federation of Hemophilia (WFH) score (representing the domain of structure and function in the ICF). In addition Canadian investigators have also developed a quality of life measure for boys with hemophilia, the Canadian Hemophilia Outcomes Kids' Life Assessment Tool or CHO-KLAT (representing the domain of participation in the ICF).