Year	Percent
1960	2.29136
1961	2.36904
1962	2.43711
1963	2.49404
1964	2.53963
1965	2.57654
1966	2.61258
1967	2.64679
1968	2.67239
1969	2.68877
1970	2.70152
1971	2.711
1972	2.72872
1973	2.76746
1974	2.83197
1975	2.91238
1976	2.98739
1977	3.05264
1978	3.1204
1979	3.19025
1980	3.25534
1981	3.31186
1982	3.34974
1983	3.36042
1984	3.34033
1985	3.29659
1986	3.24853
1987	3.19517
1988	3.12023
1989	3.02227
1990	2.91175
1991	2.79476
1992	2.68793
1993	2.60533
1994	2.55384
1995	2.52248
1996	2.49981
1997	2.46941
1998	2.42323
1999	2.35558
2000	2.27638
2001	2.19779
2002	2.13293
2003	2.08605
2004	2.06176
2005	2.0542
2006	2.04785
2007	2.04084
2008	2.04443
2009	2.05936
2010	2.07976
2011	2.10255
2012	2.11727
2013	2.11399
2014	2.08779
2015	2.04541
2016	1.99856
2017	1.95408