Year	Percent
1968	0.9548
1969	0.8867
1970	0.9232
1971	0.9104
1972	1.0653
1973	0.9752
1974	1.073
1975	1.5906
1976	1.758
1977	1.6486
1978	1.8312
1979	1.6154
1980	1.4908
1981	1.7208
1982	1.7551
1983	1.9868
1984	1.9096
1985	1.8757
1986	1.9562
1987	2.0352
1988	1.7201
1989	1.4826
1990	1.3619
1991	1.3629
1992	1.4386
1993	1.7041
1994	2.0463
1995	2.3095
1996	2.4549
1997	2.5191
1998	3.1298
1999	3.6995
2000	3.8287
2001	4.2264
2002	4.6672
2003	4.5754
2004	4.3341
2005	3.9936
2006	3.905
2007	3.5801
2008	3.728
2009	4.9072
2010	4.9689
2011	4.443
2012	4.2917
2013	4.1475
2014	3.588
2015	3.4864
2016	3.1997
2017	2.862