Year	Percent
1960	2.29571
1961	2.39171
1962	2.49827
1963	2.60059
1964	2.69544
1965	2.78306
1966	2.87575
1967	2.97209
1968	3.0623
1969	3.13592
1970	3.20746
1971	3.25887
1972	3.31148
1973	3.39822
1974	3.52623
1975	3.66825
1976	3.8034
1977	3.89481
1978	3.92013
1979	3.8679
1980	3.76491
1981	3.65208
1982	3.54691
1983	3.43959
1984	3.33416
1985	3.23237
1986	3.12088
1987	3.01124
1988	2.92321
1989	2.86272
1990	2.81803
1991	2.77828
1992	2.72261
1993	2.63426
1994	2.50592
1995	2.35184
1996	2.20395
1997	2.07152
1998	1.93459
1999	1.7948
2000	1.66143
2001	1.52704
2002	1.41551
2003	1.36074
2004	1.37555
2005	1.43941
2006	1.51796
2007	1.58881
2008	1.65448
2009	1.70809
2010	1.75154
2011	1.79401
2012	1.83435
2013	1.85845
2014	1.86486
2015	1.85598
2016	1.84167
2017	1.82311