Courses on this subject have grown significantly in the last couple of decades.[14] Teaching accountants about ethics can involve role playing, lectures, case studies, guest lectures, as well as other mediums.[9] Recent studies indicate that nearly all accounting textbooks touch on ethics in some way.[15] In 1993, the first United States center that focused on the study of ethics in the accounting profession opened at Binghamton University.[16] Starting in 1999, several U.S. states began requiring ethics classes prior to taking the CPA exam.[15][17]