Year	Percent
1960	7.12354
1961	8.1762
1962	8.99905
1963	9.25223
1964	9.05603
1965	8.59736
1966	8.09814
1967	7.76969
1968	7.69868
1969	7.91138
1970	8.21802
1971	8.66278
1972	8.89535
1973	8.58891
1974	7.75059
1975	6.73529
1976	5.57308
1977	4.83255
1978	5.15418
1979	6.6556
1980	8.61054
1981	10.33681
1982	11.14369
1983	10.94442
1984	9.83257
1985	8.32045
1986	6.98608
1987	5.95319
1988	4.95474
1989	3.9923
1990	3.10688
1991	2.29195
1992	1.63298
1993	1.21335
1994	1.09632
1995	1.2464
1996	1.70874
1997	2.3284
1998	2.9166
1999	3.39659
2000	3.92918
2001	4.07267
2002	4.55873
2003	6.43687
2004	9.71705
2005	13.07604
2006	15.55126
2007	16.33164
2008	15.51854
2009	13.53942
2010	11.22069
2011	9.24508
2012	7.7601
2013	6.46572
2014	5.36124
2015	4.41262
2016	3.49507
2017	2.66504