Year	Percent
1960	2.57255
1961	2.58428
1962	2.59504
1963	2.6054
1964	2.616
1965	2.62698
1966	2.64762
1967	2.67026
1968	2.67986
1969	2.67288
1970	2.66106
1971	2.65524
1972	2.67229
1973	2.72235
1974	2.81158
1975	2.92988
1976	3.03089
1977	3.13075
1978	3.28335
1979	3.49643
1980	3.72947
1981	3.92874
1982	4.05825
1983	4.12029
1984	4.10655
1985	4.02564
1986	3.96356
1987	3.86421
1988	3.60273
1989	3.15548
1990	2.61101
1991	2.02363
1992	1.53096
1993	1.24602
1994	1.23642
1995	1.41401
1996	1.64944
1997	1.81425
1998	1.87994
1999	1.80216
2000	1.62997
2001	1.44801
2002	1.31319
2003	1.2126
2004	1.16217
2005	1.14928
2006	1.13813
2007	1.12137
2008	1.12433
2009	1.14927
2010	1.18708
2011	1.23163
2012	1.26625
2013	1.27602
2014	1.25216
2015	1.20352
2016	1.14879
2017	1.09684