Many countries rely heavily on patients' out-of-pocket payments to providers to finance their health care systems. This prevents some people from seeking care and results in financial catastrophe and impoverishment for others who do obtain care. Surveys in eighty-nine countries covering 89 percent of the world's population suggest that 150 million people globally suffer financial catastrophe annually because they pay for health services. Prepayment mechanisms protect people from financial catastrophe, but there is no strong evidence that social health insurance systems offer better or worse protection than tax-based systems do.