Year	Percent
1960	7.62901
1961	8.66401
1962	9.47447
1963	9.7142
1964	9.3802
1965	8.91126
1966	8.40715
1967	8.07287
1968	7.99491
1969	8.20147
1970	8.50253
1971	8.94113
1972	8.98309
1973	8.67565
1974	7.83706
1975	6.82221
1976	5.65851
1977	4.91694
1978	5.23814
1979	6.73991
1980	8.78173
1981	10.50584
1982	11.31
1983	11.1091
1984	9.99387
1985	8.48049
1986	7.31861
1987	6.67615
1988	5.62774
1989	4.61871
1990	3.68948
1991	2.83475
1992	2.13779
1993	1.68139
1994	1.53173
1995	1.65142
1996	2.08484
1997	2.64576
1998	3.15558
1999	3.6227
2000	4.14326
2001	4.27498
2002	4.75134
2003	6.61859
2004	9.946
2005	13.39076
2006	15.83319
2007	16.58321
2008	15.74498
2009	13.73995
2010	11.38838
2011	9.34753
2012	7.8564
2013	6.55487
2014	5.44523
2015	4.49046
2016	3.56576
2017	2.72864