Year	Percent
1960	6.34304
1961	6.19002
1962	6.21039
1963	6.08213
1964	5.89907
1965	5.7568
1966	5.58872
1967	5.57679
1968	5.31332
1969	4.92079
1970	4.64822
1971	4.53993
1972	4.62464
1973	4.38774
1974	4.53375
1975	4.77538
1976	4.62862
1977	4.40305
1978	4.23291
1979	4.18526
1980	4.48946
1981	4.45714
1982	4.8127
1983	4.82661
1984	4.92605
1985	4.75848
1986	4.52517
1987	4.19144
1988	3.76897
1989	3.61396
1990	3.56232
1991	3.68179
1992	3.45634
1993	3.21123
1994	3.02457
1995	2.5939
1996	2.47589
1997	2.32107
1998	2.27079
1999	2.20624
2000	2.15578
2001	2.19026
2002	2.25657
2003	2.31408
2004	2.25903
2005	2.19893
2006	2.14622
2007	2.15417
2008	2.28191
2009	2.44669
2010	2.39055
2011	2.31025
2012	2.21072
2013	2.09088
2014	1.97213
2015	1.88258
2016	1.83868
2017	1.83484