Year	Percent
1960	1.69692
1961	1.97315
1962	2.22561
1963	2.38779
1964	2.44579
1965	2.4061
1966	2.34696
1967	2.31865
1968	2.28605
1969	2.24715
1970	2.21445
1971	2.18047
1972	2.14764
1973	2.12037
1974	2.11575
1975	2.13835
1976	2.1544
1977	2.16951
1978	2.18469
1979	2.19789
1980	2.22267
1981	2.23352
1982	2.2481
1983	2.26602
1984	2.2711
1985	2.26528
1986	2.25621
1987	2.22857
1988	2.23374
1989	2.25946
1990	2.29464
1991	2.33006
1992	2.31944
1993	2.26114
1994	2.11175
1995	1.91362
1996	1.70224
1997	1.50357
1998	1.3048
1999	1.09461
2000	0.88981
2001	0.68778
2002	0.49366
2003	0.34234
2004	0.24382
2005	0.19147
2006	0.15518
2007	0.13039
2008	0.11325
2009	0.12317
2010	0.13368
2011	0.14665
2012	0.18458
2013	0.25098
2014	0.36846
2015	0.51431
2016	0.67695
2017	0.81498