Year	Percent
1970	0.58191
1971	0.61546
1972	0.6331
1973	0.65998
1977	0.72204
1978	0.75336
1979	0.74568
1980	0.74353
1981	0.75178
1982	0.74738
1983	0.70133
1984	0.67651
1986	0.79799
1987	0.81294
1989	0.83242
1990	0.78217
1999	0.82335
2000	0.81514
2001	0.82727
2002	0.81157
2004	0.82804
2005	0.83965
2006	0.84908
2007	0.85559
2008	0.87302
2009	0.88793
2010	0.89716
2011	0.90808
2012	0.9543
2013	0.9525