Hawaii's health care system insures over 95% of residents. Under the state's plan, all businesses are required to provide employees who work more than twenty hours per week with health care. Heavy regulation of insurance companies helps keep the cost to employers down. In addition, due in part to the system's emphasis on preventive care, Hawaiians require hospital treatment less frequently than their counterparts in the rest of the United States, while total health care expenses (measured as a percentage of state GDP) are substantially lower. Given these achievements, proponents of universal health care elsewhere in the U.S. have sometimes used Hawaii as a model for proposed federal and state health care plans. Critics, however, claim that Hawaii's success is due at least in part to its mild climate and to its status as a chain of islands whose economy is heavily based on tourism: features that make it more difficult for businesses unhappy with paying the plan's premiums to relocate elsewhere.