Year	Percent
1960	3.17186
1961	3.27661
1962	3.38307
1963	3.49099
1964	3.60054
1965	3.71094
1966	3.82407
1967	3.93427
1968	4.0395
1969	4.14195
1970	4.24129
1971	4.33798
1972	4.50871
1973	4.76529
1974	5.04528
1975	5.35535
1976	5.69601
1977	6.06984
1978	6.49876
1979	7.00691
1980	7.38071
1981	7.85462
1982	8.43343
1983	9.10106
1984	9.81563
1985	10.52326
1986	11.20847
1987	11.81043
1988	12.29926
1989	12.59098
1990	12.64843
1991	12.45759
1992	12.09681
1993	11.70519
1994	11.41448
1995	11.27922
1996	11.30671
1997	11.45325
1998	11.66012
1999	11.84342
2000	11.94953
2001	11.96424
2002	11.92363
2003	11.87157
2004	11.75034
2005	11.5879
2006	11.50168
2007	11.47027
2008	11.46714
2009	11.45674
2010	11.4189
2011	11.34908
2012	11.26006
2013	11.16623
2014	11.08818
2015	11.03714
2016	11.01465
2017	11.01404