Year	Percent
1960	8.15652
1961	9.91801
1962	11.83725
1963	12.1294
1964	10.9043
1965	9.23667
1966	7.51746
1967	6.89759
1968	7.97218
1969	10.66881
1970	14.44706
1971	16.88188
1972	17.68954
1973	17.69552
1974	17.12544
1975	16.2121
1976	15.5798
1977	14.78389
1978	13.28648
1979	11.32124
1980	9.31401
1981	7.22874
1982	5.67452
1983	4.92926
1984	4.81315
1985	5.08044
1986	5.4452
1987	5.65909
1988	5.7367
1989	5.69453
1990	5.57742
1991	5.5541
1992	5.56558
1993	5.44072
1994	5.16151
1995	4.8414
1996	5.0916
1997	5.4606
1998	5.54538
1999	5.69352
2000	5.96299
2001	5.80236
2002	5.81424
2003	6.97583
2004	9.33223
2005	11.83287
2006	13.97874
2007	14.68949
2008	13.59894
2009	11.04026
2010	7.99823
2011	5.1425
2012	2.9802
2013	1.55516
2014	1.07735
2015	1.26522
2016	1.59084
2017	1.72702