Year	Percent
1971	0.71013
1972	0.73044
1973	0.73797
1974	0.74888
1975	0.7515
1976	0.76253
1977	0.7703
1978	0.77387
1979	0.78423
1980	0.78932
1981	0.78898
1982	0.79394
1983	0.79331
1984	0.79664
1985	0.79748
1986	0.80351
1987	0.80968
1988	0.81367
1989	0.81669
1990	0.82109
1991	0.82784
1992	0.87079
1995	0.84699
1997	0.85468
1998	0.80691
1999	0.8274
2001	0.85522
2002	0.80243
2003	0.8503
2004	0.84338
2005	0.82878
2006	0.8304
2007	0.84029
2008	0.84489
2009	0.85854
2011	0.86355
2012	0.8712
2014	0.87856
2015	0.88486
2016	0.8869