Year	Percent
1968	0.9877
1969	0.9796
1970	0.813
1971	0.9934
1972	1.0552
1973	1.0008
1974	1.2298
1975	1.6781
1976	1.5567
1977	1.7844
1978	2.0083
1979	1.9009
1980	1.9463
1981	1.9231
1982	2.0888
1983	2.4825
1984	2.6515
1985	2.5094
1986	2.6168
1987	2.599
1988	2.3853
1989	2.1674
1990	2.0735
1991	2.0552
1992	2.1053
1993	2.4005
1994	2.8488
1995	3.018
1996	3.0495
1997	3.2824
1998	3.8939
1999	4.3527
2000	4.321
2001	4.6256
2002	5.1581
2003	4.9162
2004	4.4557
2005	4.4143
2006	3.9138
2007	3.868
2008	4.0479
2009	5.0511
2010	4.7727
2011	4.413
2012	4.169
2013	3.9466
2014	3.5971
2015	3.3149
2016	3.0735
2017	2.7568