Year	Percent
1971	0.43451
1972	0.44197
1974	0.4517
1984	0.60605
1991	0.69501
1992	0.75943
1993	0.7451
1994	0.67534
1995	0.63605
1996	0.60513
1999	0.62296
2000	0.65729
2001	0.68761
2002	0.69795
2003	0.70012
2004	0.73525
2005	0.78271
2006	0.81403
2007	0.83603
2008	0.86237
2009	0.89179
2010	0.90081
2011	0.91161
2012	0.92194
2015	0.92034