Year	Percent
1971	0.47031
1972	0.48347
1973	0.54137
1974	0.56635
1975	0.57472
1976	0.59381
1977	0.60978
1978	0.60465
1979	0.61743
1980	0.61908
1981	0.61995
1982	0.60625
1983	0.61483
1984	0.63428
1985	0.65855
1986	0.6805
1987	0.71118
1988	0.75333
1989	0.7696
1990	0.77789
1991	0.80659
1992	0.78899
1993	0.79101
2003	0.78355
2004	0.80082
2005	0.81616
2006	0.85834
2007	0.86892
2009	0.89156
2010	0.90326
2011	0.91821
2012	0.9305
2013	0.94201
2014	0.96531
2015	0.97921
2016	0.99158