Year	Percent
1960	10.30088
1961	8.91613
1962	8.77929
1963	10.55591
1964	12.81657
1965	13.3093
1966	10.75717
1967	12.94118
1968	15.14437
1969	11.40842
1970	12.82563
1971	14.38432
1972	12.12583
1973	13.68519
1974	18.59877
1975	16.09479
1976	21.40517
1977	20.03832
1978	21.61895
1979	18.74511
1980	15.86556
1981	17.03166
1982	14.14477
1983	11.07182
1984	11.57233
1985	11.49742
1986	10.33274
1987	13.91056
1988	13.6992
1989	13.51511
1990	13.60261
1991	14.29528
1992	18.32532
1993	17.24629
1994	15.6813
1995	15.05511
1996	12.68678
1997	13.68454
1998	17.39552
1999	17.35399
2000	17.83539
2001	19.65917
2002	20.55393
2003	20.3006
2004	20.84655
2005	19.73588
2006	20.82414
2007	20.83121
2008	16.40208
2009	13.05306
2010	13.93751
2011	15.22916
2012	14.95454
2013	14.00861
2014	13.70603
2015	13.62469
2016	12.88761
2017	12.0644