Year	Percent
1960	8.46221
1961	8.70528
1962	8.71312
1963	8.68829
1964	8.66382
1965	8.59994
1966	8.57548
1967	8.57105
1968	8.59473
1969	8.61662
1970	8.69187
1971	8.73486
1972	8.79739
1973	8.92807
1974	9.17601
1975	9.44967
1976	9.68639
1977	9.8032
1978	9.84826
1979	9.79288
1980	9.66288
1981	9.51221
1982	9.33561
1983	9.00394
1984	8.52218
1985	7.95085
1986	7.31881
1987	6.76193
1988	6.46888
1989	6.47958
1990	6.65814
1991	6.93548
1992	7.02408
1993	6.65535
1994	4.51921
1995	2.54011
1996	1.43048
1997	0.55637
1998	0.06545
1999	0.1071
2000	0.55013
2001	1.14663
2002	1.67863
2003	2.13206
2004	2.90742
2005	3.47911
2006	3.59607
2007	3.80613
2008	4.30026
2009	5.12545
2010	6.06966
2011	7.58979
2012	8.5845
2013	8.56708
2014	8.09311
2015	7.3485
2016	6.62149
2017	5.94586