Year	Percent
1960	3.725
1961	4.024
1962	4.347
1963	4.694
1964	5.069
1965	5.47
1966	5.902
1967	6.712
1968	7.625
1969	8.649
1970	9.796
1971	11.078
1972	11.3
1973	11.507
1974	11.717
1975	11.93
1976	12.147
1977	12.366
1978	12.59
1979	12.817
1980	13.047
1981	13.242
1982	13.428
1983	13.616
1984	13.806
1985	13.998
1986	14.193
1987	14.39
1988	14.589
1989	14.791
1990	14.994
1991	14.816
1992	14.629
1993	14.445
1994	14.262
1995	14.081
1996	13.901
1997	13.724
1998	13.549
1999	13.375
2000	13.204
2001	13.182
2002	13.164
2003	13.146
2004	13.127
2005	13.109
2006	13.091
2007	13.073
2008	13.055
2009	13.037
2010	13.019
2011	13
2012	12.982
2013	12.978
2014	12.988
2015	13.012
2016	13.05
2017	13.102