Year	Percent
1960	8.28894
1961	7.25457
1962	5.21763
1963	4.49963
1964	5.50048
1965	6.89784
1966	8.29217
1967	9.08687
1968	9.02424
1969	8.12452
1970	6.82431
1971	5.57598
1972	4.64355
1973	3.9563
1974	3.58387
1975	3.43884
1976	3.31044
1977	3.18111
1978	3.22031
1979	3.43278
1980	4.96241
1981	5.95161
1982	6.20591
1983	6.31905
1984	6.26255
1985	6.0985
1986	5.85433
1987	5.67167
1988	5.70779
1989	5.99993
1990	6.40665
1991	6.85042
1992	7.07172
1993	6.86228
1994	6.18484
1995	4.54533
1996	3.10579
1997	2.4429
1998	1.97659
1999	1.76641
2000	1.75941
2001	1.77165
2002	1.81049
2003	2.06113
2004	2.55636
2005	4.64923
2006	5.63094
2007	5.98674
2008	6.26947
2009	6.44483
2010	6.51754
2011	6.57267
2012	6.52207
2013	6.19235
2014	5.57451
2015	4.18018
2016	3.46246
2017	2.83992