Year	Percent
1960	10.37807
1961	10.4656
1962	10.54192
1963	10.51363
1964	10.37597
1965	10.15189
1966	6.5969
1967	6.51666
1968	6.53797
1969	6.68469
1970	6.90823
1971	7.12142
1972	7.27704
1973	7.34479
1974	7.34572
1975	7.55627
1976	8.79542
1977	8.65076
1978	8.51602
1979	5.07612
1980	5.01557
1981	4.95105
1982	4.87849
1983	4.7812
1984	4.66256
1985	4.52999
1986	4.3875
1987	4.26435
1988	4.28683
1989	4.51671
1990	4.49774
1991	4.48008
1992	4.43444
1993	4.359
1994	4.24731
1995	4.10894
1996	3.98802
1997	3.86403
1998	3.69652
1999	3.52115
2000	3.30638
2001	3.04934
2002	2.84519
2003	2.72673
2004	2.7219
2005	2.78983
2006	2.88089
2007	2.9595
2008	3.04343
2009	3.12064
2010	3.19681
2011	3.27803
2012	3.35129
2013	3.39518
2014	3.40242
2015	3.40264
2016	3.39029
2017	3.38392