Year	Percent
1960	2.2753
1961	2.35541
1962	2.43674
1963	2.50404
1964	2.55938
1965	2.61333
1966	2.68269
1967	2.78271
1968	2.90799
1969	3.06155
1970	3.24714
1971	3.4116
1972	3.5943
1973	3.86666
1974	4.24057
1975	4.65237
1976	5.01851
1977	5.28863
1978	5.47155
1979	5.56027
1980	5.56863
1981	5.57694
1982	5.53964
1983	5.35627
1984	5.01363
1985	4.59819
1986	4.10359
1987	3.6897
1988	3.53295
1989	3.68798
1990	3.99679
1991	4.40506
1992	4.61804
1993	4.38174
1994	3.61685
1995	2.56659
1996	1.45841
1997	0.5843
1998	0.09339
1999	0.13504
2000	0.57808
2001	1.17456
2002	1.70656
2003	2.16004
2004	2.46372
2005	2.68449
2006	2.81598
2007	3.04159
2008	3.55094
2009	4.39379
2010	5.35264
2011	6.23921
2012	6.78801
2013	6.88211
2014	6.50466
2015	5.85617
2016	5.21772
2017	4.66919