Year	Percent
1971	0.5683
1972	0.57884
1973	0.58563
1974	0.58964
1975	0.59562
1976	0.58956
1977	0.57704
1979	0.58689
1980	0.60068
1981	0.58929
1982	0.59247
1983	0.58844
1984	0.58849
1985	0.59104
1986	0.58922
1994	0.63895
1999	0.68411
2000	0.70023
2001	0.71276
2003	0.73722
2004	0.7666
2005	0.78233
2006	0.79949
2007	0.81793
2008	0.83998
2009	0.85607
2010	0.87711
2011	0.89341
2012	0.91462
2013	0.93689
2014	0.94829
2015	0.96035
2016	0.97131