Year	Percent
1971	0.42148
1973	0.49439
1974	0.5267
1975	0.54412
1976	0.51883
1982	0.7147
1983	0.72223
1984	0.71834
1985	0.71022
1986	0.7052
1987	0.71461
1988	0.72321
1989	0.72494
1992	0.71479
1993	0.77697
1994	0.76689
1995	0.75572
1996	0.74704
1997	0.73816
1999	0.71782
2000	0.71398
2001	0.71128
2002	0.7202
2004	0.75874
2005	0.7626
2006	0.76483
2007	0.80112
2008	0.80654
2009	0.82387
2011	0.85888
2012	0.83738
2013	0.82627
2014	0.84121
2015	0.84511
2016	0.85291
2017	0.86261