Year	Percent
1960	3.54043
1961	3.31042
1962	3.07908
1963	2.84461
1964	2.62987
1965	2.45423
1966	2.29381
1967	2.20872
1968	2.3141
1969	2.65078
1970	3.13511
1971	3.56087
1972	3.93539
1973	4.42675
1974	5.04097
1975	5.64597
1976	6.2565
1977	6.62096
1978	6.48055
1979	5.80257
1980	4.86515
1981	3.87837
1982	3.11312
1983	2.68522
1984	2.68108
1985	2.95259
1986	3.29536
1987	3.51125
1988	3.5509
1989	3.35826
1990	3.03824
1991	2.7513
1992	2.5798
1993	2.47837
1994	2.46374
1995	2.53515
1996	2.62085
1997	2.77148
1998	3.10657
1999	3.65456
2000	4.31513
2001	4.83663
2002	5.24991
2003	5.75681
2004	6.36026
2005	6.90436
2006	7.49936
2007	7.77374
2008	7.32247
2009	6.12806
2010	4.60391
2011	2.97005
2012	1.70244
2013	1.1618
2014	1.5828
2015	2.61867
2016	3.8128
2017	4.6217