Year	Percent
1960	3.48021
1961	3.59782
1962	3.68161
1963	3.77425
1964	7.22934
1965	17.36703
1966	17.35156
1967	17.36975
1968	17.36639
1969	17.27717
1970	17.21519
1971	17.11169
1972	10.77269
1973	10.23442
1974	10.31319
1975	10.40334
1976	10.48305
1977	10.49641
1978	10.45853
1979	10.33488
1980	10.1676
1981	9.95984
1982	14.01538
1983	14.29171
1984	13.87977
1985	13.40589
1986	12.9459
1987	12.4488
1988	11.96468
1989	11.45193
1990	10.97585
1991	10.48401
1992	5.23219
1993	4.43311
1994	4.28123
1995	4.09829
1996	3.92241
1997	3.75699
1998	3.59409
1999	3.42536
2000	3.26571
2001	3.09868
2002	2.35075
2003	2.19841
2004	2.2062
2005	2.25783
2006	2.32972
2007	4.26202
2008	4.23785
2009	4.18869
2010	4.14321
2011	4.09544
2012	3.23838
2013	3.09216
2014	3.07148
2015	3.03476
2016	2.99353
2017	2.94584