Co-payments were introduced in the 1980s in an attempt to prevent over utilization. The average length of hospital stay in Germany has decreased in recent years from 14 days to 9 days, still considerably longer than average stays in the United States (5 to 6 days). Part of the difference is that the chief consideration for hospital reimbursement is the number of hospital days as opposed to procedures or diagnosis. Drug costs have increased substantially, rising nearly 60% from 1991 through 2005. Despite attempts to contain costs, overall health care expenditures rose to 10.7% of GDP in 2005, comparable to other western European nations, but substantially less than that spent in the U.S. (nearly 16% of GDP).