Year	Percent
1973	0.52262
1977	0.66963
1978	0.67262
1979	0.67344
1981	0.70395
1982	0.7148
1983	0.70526
1985	0.7302
1986	0.73797
1987	0.74373
1990	0.7271
1991	0.70814
1992	0.71258
1993	0.70174
1994	0.68757
1995	0.68573
1999	0.72855
2000	0.74311
2001	0.75984
2002	0.77847
2004	0.81818
2005	0.82852
2006	0.845
2007	0.85224
2008	0.86293
2009	0.87999
2010	0.88659
2011	0.89785
2012	0.90373
2013	0.90872
2014	0.91458
2015	0.91537