Year	Percent
1971	0.52216
1972	0.53096
1973	0.57331
1974	0.54467
1976	0.52707
1978	0.53319
1979	0.53986
1980	0.53678
1981	0.54809
1982	0.54914
1983	0.55095
1984	0.55279
1987	0.57505
1988	0.57042
1989	0.58962
1990	0.58383
1991	0.58549
1992	0.57278
1993	0.59786
1994	0.61092
1995	0.64675
1996	0.63853
1997	0.63311
1998	0.66574
1999	0.67813
2000	0.70376
2003	0.7123
2004	0.73416
2005	0.74574
2006	0.75883
2007	0.7783
2008	0.78251
2009	0.79074
2010	0.80729
2011	0.81824
2014	0.83934
2015	0.86426
2016	0.83802