Sex reassignment surgery statistics are difficult to verify due to the fact that many patients choose to have their surgeries outside the United States and UK. Sex change operations are extremely expensive and this cost forces many people to travel to clinics in other countries that offer sex reassignment services. In the United States and the UK sex change surgery is difficult for patients to afford because it is not supported by insurance and it is tricky to find a surgeon trained in the procedures. Fortunately, many surgeons are currently training to become qualified as sex reassignment surgeons. The Standards of Care for gender disorders are overseen by the World Professional Association for Transgender Health which promotes training and knowledge for surgeons around the globe. The association sets standards for doctors to follow concerning pre-operative and post-operative surgical procedures as well as surgery. Medical boards in the United States and other countries follow the association's recommendations such as length of time in pre-operative therapy and length of time spent living as the chosen gender before surgery.